In this study 3 to 28 days old calves (n=36) with a systemic acidosis (venous blood pH <7,30) following gastrointestinal and/or respiratory disease were examined. The objectives were (1) to investigate the pathogenesis of the acidosis, (2) to describe the compensatory reactions of the acid-base disorders, (3) to determine the correlations between clinical symptoms and the acid-base- status, (4) to evaluate the compatibility and effectiveness of the buffers Carbicarb and Tribonate compared to NaHCO3 and (5) to evaluate the TCO2-determination in blood with the Harleco apparatus for the diagnosis of metabolic acid-base disorders in calves. On entry n=10 (27,7%) calves showed a marked respiratory compensation (PvCO2 <5,3 kPa) of the underlying metabolic acidosis (ABE: x ±s = -22,1 ± 5,3). In n=15 (41,6%) calves the PvCO2 was between 5,3 and 6,7 kPa (ABE: x ±s = -15,4 ± 7,6) and in n=11 (30,6%) calves the PvCO2 was >6,7 kPa (ABE: x ±s = -10,2 ± 13,1). Therefore the acidosis of the calves with a PvCO2 >6,7 kPa was partly of mixed respiratory-metabolic origin. Between the clinical symptoms as ability to stand, rectal temperature, enophthalmus, corneal reflex, suckle reflex and the laboratory data of the acid-base status pH, ABE, HCO3- and PvCO2 only low correlation coefficients were found (rs <0,5). The highest correlation was found between the behavioral status of the calves and the pH (rs = -0,5427). Although it would be desirable for the daily routine practice, the estimation or accurate diagnosis of the acidosis alone on the basis of clinical symptoms, prooved not to be sufficient. For the treatment of the acidosis the calves were randomly assigned to three treatment groups. Besides NaHCO3 the buffer mixtures Carbicarb and Tribonate were used. Carbicarb is an equimolar mixture of NaHCO3 (333 mmol/l) and Na2CO3 (333 mmol/l). Tribonate is a mixture of Tris-buffer (300 mmol/l), acetate (200 mmol/l), NaHCO3 (160 mmol/l) and Na2HPO4 (20 mmol/l). To compare their effectiveness the buffers were equilibrated with 0,9% NaCl and destilled water to achieve isotonicity and a final concentration of 100 mmol buffer anions in 1 Liter (= one treatment) of the infusion solutions. The buffers exhibited different impacts on the calves acid-base equilibrium. Carbicarb followed by Tribonate and NaHCO3, had the greatest alkalizing potential. With each application of 100 mmol buffer anions the average rise of blood pH was x ±s = 0,09 ± 0,05 pH units with Carbicarb, 0,08 ± 0,03 with Tribonate and 0,06 ± 0,02 with NaHCO3. For the metabolic parameters of acid- base status HCO3- and TCO2, a significant stronger alkalizing effect was found with Carbicarb. Overcorrection of the pH towards an alkalosis occured once in n=43 treatments with Carbicarb and once in n=51 treatments with Tribonate although high dilutions of the buffers were used. The three buffers also showed a different influence on the PvCO2 as the respiratory component of acid-base status. With Tribonate there was a decline in the mean value of PvCO2 from x ±s = 6,5 ± 1,9 kPa at the beginning of buffer therapy to x ±s = 5,2 ± 1,4 kPa after 200 mmol of buffer anions had been given. A sudden decline of the PvCO2 could lead to a respiratory depression as CO2 is the principal regulator of respiration. With NaHCO3 a small and transitory increase of the PvCO2 was seen. This rise in CO2 with NaHCO3 has to be eliminated by increased ventilation. In cases of impaired pulmonary elimination of CO2 a consecutive accumulation of CO2 in the body with the development of a paradoxical intracellular and cerebrospinal acidosis may be expected with NaHCO3. With Carbicarb there was more or less no obvious effect on the PvCO2. In future, the different effectiveness of the tested buffers could be used according to the individual pathogenesis of an acidotic disturbance. For the treatment of a simple metabolic acidosis with respiratory compensation the use of NaHCO3 is advised. For the treatment of a mixed respiratory-metabolic acidosis e.g. in asphyxia, Carbicarb may be promising. The TCO2 values of n=376 venous blood samples of the study calves obtained with the Harleco apparatus and a conventional blood-gas-analyzer were compared. Using the standard solution the correlation coefficients between the two methods for the determination of the TCO2 in whole blood were r = 0,8657 and r = 0,9015 in plasma. The simplified method of analysis without using the standard solution showed higher correlations in whole blood (r = 0,9116) and in plasma (r = 0,9529). There was a linear relationship between the TCO2-determination with the Harleco-apparatus and the blood-gas-analyzer. The gradient of the regression lines (b = 0,53-0,75) showed a bias of the Harleco-method. Samples with a small TCO2-content were classified too high by the Harleco-apparatus which means that the acidosis was underestimated. Samples with high TCO2-values were classified too low which means that the alkalotic deviation of the blood sample was underestimated. Therefore the Harleco-TCO2-values were corrected with the regression equations. With the use of the standard solution the rate of the correct allocations into corresponding categories of the blood-gas- analyzer-TCO2 was 40% to 72% for whole blood and 51% to 82% for plasma. Without using the standard solution a higher rate of correct diagnosis by the Harleco-TCO2 from 50% to 82% with whole blood and from 59% to 91% with plasma was achieved. For the diagnosis of metabolic acidosis in calves the determination of TCO2 with the Harleco-apparatus offers a simple and cheap alternative to conventional blood gas analysis for the veterinary practitioner. By applying a simplified method of analysis without using the standard solution a higher precision of the Harleco-TCO2-determination was achieved.