We have performed intensive research in recent years into paratuberculosis infection within our herds of ruminants. This experience, together with diagnostic testing has been used to a farm control programme performed for more than 3,000 cows on more than 15 farms and 400 sheep on one farm. The results of sensitivity and specificity have been obtained based on culture examinations of 21,148 faecal samples and laboratory tests of organs from 1,943 cattle and 370 sheep. Clinical signs such as diarrhoea and weight loss were seen in only 5 to 15% of the infected animals. Mycobacterium avium subsp. paratuberculosis was detected in 68.8% of cattle with diarrhoea and weight loss, and in 50% of sheep with weight loss. The occurrence of these clinical signs were more frequent, especially during the feed-transition from winter to summer and also after parturition. Clinical disease occurred most often in cattle aged 2 to 6 years. Using allergenodiagnosis 26.8% sensitivity at 72.0% specificity were obtained using avian tuberculin and 22.2% and 67.7% using Johnin. Examination of 3,026 allergologically reacting animals from infection-free herds showed a 99.4% AGID specificity, and 762 animals examined by ELISA showed a 93.3% specificity. Sensitivity of these methods and CFT was dependent on the level of animal infection. In the course of the development of the disease, the sensitivity of the examinations by AGID, CFT and ELISA increased from 18-20% to 80-90%. In clinically healthy animals with confirmed excretion (low shedders), the disease could not be serological diagnosed in more than 85% of animals by AGID, CFT and ELISA, also sensitivity correlated to the extent of excretion. Faecal cultures were negative in 25.0% animals with positive findings in mesenteric lymphatic nodes and intestinal mucous.