Epizootiological analysis for the occurrence of enzootic bovine leukaemia (EBL) performed on 35 660 cattle in private farms situated in the Wrocław region showed that 5% of the animals were positive. In 1992 EBL was diagnosed in only 34 out of 98 farms by the AGID test in which in 1988-1990 a nodular form of leukaemia was found. Farms with large herds serve as a reservoir of BLV because about 47% serologically confirmed cases of EBL in private farms were connected with purchasing cattle from such farms. The frequency of EBL was twice as high in the regions where the same veterinary staff serviced both the private and state farms compared to regions where the veterinary staff exclusively serviced private farmers. These observations point to a iatrogenic route of BLV transmission.