The purpose of the study was to carry out serological examinations in foxes originating from farms with unsatisfied reproduction results located in the Silesia, Lublin, Mazowsze, Pomorze, Mazury and Wielkopolska districts. Moreover, the same examinations were conducted in reference to sera of mink with bad reproduction findings. Out of 435 sera from 17 fox farms, HI antibodies were found in 28.6 per cent. Specific antibodies were also recorded in 2 of 3 mink farms. Of 132 sera, the antibodies were found in 72 samples (54.5 per cent). In addition, from 19 samples of faeces, homogenized internal organs of 7 foetuses and the uterus of a pregnant mink, a parvovirus was isolated (their HA=640-2560). A marked distribution of parvovirus infections in foxes indicates that vaccination should be carried out in the animals before copulation. However, others reasons, such as unsatisfactory nutrition, could influence bad reproduction results.