Selected haematological and biochemical parameters in blood of lambs born to maedi-visna virus (MVV) seropositive and seronegative ewes were investigated. The study included 116 lambs born to ewes with MVV antibodies and 111 lambs born from seronegative mothers. The presence of antibodies was determined by ELISA. Blood samples were taken prior to weaning and post-weaning at 18-23 and 80-88 d of age, respectively. The study revealed that age and serological status had a significant effect on most of investigated variables. Lambs from seropositive ewes had significantly lower average white cell counts (P<0.05) than lambs from seronegative ones. A similar relationship was noted for lymphocyte counts; however, granulocyte count was higher in the litter of uninfected ewes. Analysis of red blood cell indices of lambs from seropositive ewes showed significantly higher haematocrit, as well as marked changes in red blood cell volume and corpuscular haemoglobin concentration, compared with those from lambs born to uninfected ewes. There were no significant differences in platelet counts in both groups of lambs, tested on days 18-23; however, significantly lower values were noted in lambs born to seropositive ewes on days 80-88. Lactate dehydrogenase and alkaline phosphatase activities and uric acid concentrations were higher in lambs from infected ewes at both time points.