Whole blood samples from 73 animals from a dairy herd infected with BLV were used for detection of proviral DNA by means of PCR technique. At the beginning 24 cows were examined with primer set ZM1/ZM2. Seven out of 13 ELISA-positive animals –were PCR-positive too and 3 were PCR-positive among 11 serologically negative. Due to unsatisfactory results the rest of the samples were tested with a second primer set ZM2/ZM3. In this study 20 cows out of 25 ELISA-positive were PCR-positive and 8 out of 24 seronegative cows were PCR-positive. The findings of seronegative PCR-positive and seropositive PCR-negative cattle indicate that further work is needed. We plan to use the nested PCR because this technique seems to be more specific and sensitive.