After the finding of paratuberculosis in imported cattle in Sweden in 1993, an increased number of diagnostic tests have been performed. In a survey, serology with an absorbed ELISA and faecal culture were performed on each imported animal. A large number of tests were also carried out for tracing on and back from known infected herds. Cattle with serological reactions in ELISA were tested with faecal culture or sent to slaughter and cultured from ileum and the ileocaecal lymph node. When Mycobacterium paratuberculosis was isolated from an animal, the whole herd was stamped out and ileum and ileocaecal lymph nodes were collected from a number of cattle at the abattoir for culture and histopathological examination. During 1993 - 1997 approximately 6000 animals were cultured and 10600 blood samples were tested in ELISA. M. paratuberculosis was isolated from 107 animals in 44 herds. Seventy-five of these animals were also tested serologically, 11 of which proved ELISA positive. Blood samples from a total of 132 animals were positive in ELISA. Forty-six of these animals were slaughtered and samples from ileum and the ileocaecal lymph node were cultured and histopathologically examined. M. paratuberculosis was isolated from 11 of these cases. Histopathological lesions were only found in cases with a strong serological reaction. The apparently low sensitivity of the absorbed ELISA in our situation may be explained by an early stage of infection in most cases. Our observations illustrate the difficulties in detecting early cases of paratuberculosis with the absorbed ELISA and the problem of optimising the use of diagnostic techniques in the tracing of infected animals.