The studies were carrid out on 70 calves coming from two farms in the Wrocław district. The calves from cows with positive serological titers (assessed by AGID) against bovine leukaemia virus (BLV). In the farms under study the last case of nodular leukaemia was observed 7 years before and the results of haematological examinations were within the normal range. Out of 7 calves aged 6 months with the presence of specific antibodies against BLV only in two cases the syncytial test appeared to be positive in previous examinations, i.e. in calves aged 1 month. Besides, the findings of serological examinations performed on calves at the age of six months indicated that the percentage of calves infected with BLV in the prenatal period was slight. Calves from cows with seropositive results can in the majority of cases avoid infection with BLV in the postnatal period by their isolation; the contacts of calves with their mothers ought to be possible only during feeding them with colostrum.