EN
A total of 193 brown hares, collected from 7 sampling sites in Poland during 1986 - 1990 were examined for genetic variability and differentiation at 39 presumptive isozyme loci by means of horizontal starch gel electrophoresis. Values of polymorphism (mean P = 0.180, SD 0.039) and average heterozygosity (mean H = 0.047, SD 0.006) were similar to those detected in previous studies on the population genetics of the brown hare. Relative (Cst = 0.041) and absolute (mean D/Nei, 1978/ = 0.0012, SD 0.0013) genetic differentiation among populations were very low, which fits well to the high number of migrant individuals per generation (Nm = 12.7), estimated using the private allele method of Slalkin (1985). Average heterozygosity was examined for associations with geographical distribution, the year of culling, population density, age, sex, body weight and health status, whereby a better survival of heterozygous femals could be detected. According Lo our results, the present decline of the brown hare is noL due to genetic depiction. However, once population sizes drop below a critical threshold, a pronounced inbreeding depression can be expected.