In this study elbow joints of 182 Bernese Mountain Dogs and 20 Great Swiss Mountain Dogs were examined clinically (by questionaire) and by X-ray in the time between August 1992 and August 1995. The dogs were younger than 13 months at the time of their first examination. Progress controls were considered up to an age of 19 months. The control examinations resulted in a total of 275 cases Bernese Mountain Dogs and in 32 cases Great Swiss Mountain Dogs. Measurements were taken on the radiographs to ascertain the size relations in the elbow joint and the degree of arthrosis. Because of the present results a possible routinely X-ray examination of the elbow joints of young Bernese Mountain Dogs and Great Swiss Mountain Dogs cannot be recommended before an age of 9 months. With the Bernese Mountain Dog 41,1% (216/525) of all joints were free of arthrosis, 21,7% (114/525) were suspicious. 19,6% (103/525) showed a low, 9,5% (50/525) a medium and 8,0% (42/525) a high degree of arthrotic changes. The joints of the Great Swiss Mountain Dog were free of arthrosis in 18% (11/61) and in 41% (25/61) suspicious. 26,2% (16/61) had a low, 9,8% (6/61) a medium and 4,9% (3/61) a high degree of arthrosis. The changes were bilateral for the Bernese Mountain Dog in 74,1% (80/108) and for the Great Swiss Mountain Dog in 64,7% (11/17) of the cases. Arthrotic changes were proved radiologic first on an age of 4 months. While the degree of arthrosis in the elbow joints of dogs under 9 months of age varied in the period of examination up to 4 degrees, it was constant in 68,8% (11/16) of the older animals, 25% (4/16) showed an increase of one degree. Lameness resulting from pain in the elbow joint was found in 22% (60/275) of the Bernese Mountain Dogs and in 15,6% (5/32) of the Great Swiss Mountain Dogs. The laming Bernese Mountain Dogs showed in 8,4% (9/107) arthrosis free, in 14% (15/107) suspicious joints, 77,6% (83/107) were affected by arthrosis (30,8% low, 21,5% medium and 25,2% to a high grade). In lamefree Bernese Mountain Dogs 51,5% (190/369) of the elbow joints were free of arthrosis, 23,6% (87/369) were suspicious and 24,9% (92/369) had arthrotic changes (16,0% a low, 6,0% a medium and 2,9% a high degree). The height of the step between radius and coronoid process of the ulna appears as suitable parameter for an early diagnosis of fragmented coronoid process. According to radiographs in mediolateral projection in 10,4% (55/529) of the elbow joints of Bernese Mountain Dogs no step was prooved. 41,6% (220/529) had a step of 1 mm, 17,8% (94/529) of 1,5 mm, 14,2% (75/529) of 2 mm, 8,3% (44/529) of 0,5 mm and 4,2% (22/529) of 3 mm height. 1,7% (9/529) showed a step of 3,5 - 4,5 mm. In the Bernese Mountain Dog 60% (33/55) of the stepless elbow joints, 48,6% (107/220) of the joints with 1 mm, 29,8% (28/94) of the joints with 1,5 mm and 21,3% (16/75) of the joints with a 2 mm step were free of arthrosis. Corresponding the percentage of arthrotic joints went up with increasing height of the step. In the course of further controls on 3 - 4 month old Bernese Mountain Dogs with arthrotic free joints a positive correlation between an average monthly increase of the height of the step and the degree of arthrosis at the control examinations was noted. At a monthly increase of the heigt of the step of 0,1 mm the joints remained free of arthrosis. At an increase of 0,33 mm a low and at an increase of 1,07 mm a high grade arthrosis was observed. The relation of the length of the trochlear notch to the length of the shortest distance between anconeal process and lateral coronoid process ("quotient") was determined as measurement for the shape of the trochlear notch and therefore for the risk of fragmentation of the coronoid process. At joints without arthrosis the trochlear notch appeared almost circular (median of the quotient on the Bernese Mountain Dog 1,15, on the Great Swiss Mountain Dog 1,22). With an increasing degree of arthrosis it became more of an elliptical form. The Bernese Mountain Dog had a quotient of 1,16 in suspicious joints, of 1,17 in joints with a low degree of arthrosis, of 1,18 with a medium degree and of 1,19 with a high degree of arthrosis (mean values). The mean values of Great Swiss Mountain Dogs were 1,24 - suspicious, 1,24 - of low degree, 1,27 - of medium degree and 1,30 - of high degree. For the Bernese Mountain Dog the mean value of the quotient was biggest at the age of 6 - 7 month (1,19). It was for male dogs (1,17) little larger than for bitches (1,16). The degree of arthrotic changes also increased with a bigger size of the elbow joint (length of trochlear notch and length of distance between the tips of anconeal process and lateral coronoid process). Additional research was done in respect of the importance of the sex, body weight and rate of growth as well as food addition of minerals for the formation of disease of the elbow joints. The epiphyseal closure in the area of the elbow joint was also documented.