From 1980 to 1983, blood was taken from 60 selected European bison (Bison bonasus) in Poland. Serum samples were tested for the presence of antibodies against Brucella abortus, 14 serovars of Leptospira interrogans, Chlamydia spp., Coxiella burnetii; foot and mouth disease virus, bovine leukemia virus and bovine herpes virus-1. In addition, an attempt was made to isolate bovine herpes virus-1 from the prepuce of selected bulls. Serological tests suggested chlamydial infection in 28 bison, subclinical Q-fever of a 2-yr-old heifer, subclinical bovine leukemia virus infection in a 12-yr-old bull and bovine herpes virus-1 infection in five bulls and three cows. Attempts to isolate bovine herpes virus-1 were not successful. These results suggest the possibility of cross transmission of several of these bovine pathogens between free-ranging bison and domestic cattle in Poland.