Relatedness and inbreeding in queens and workers of the polygynous ant Myrmica rubra were estimated using an isozyme polymorphism. Samples were taken from a polydomous and a non-polydomous population in two two-year periods separated by five years. In both periods significant queen relatedness was found in nests of the non-polydomous population in the second year. In the first years, and in the polydomous population, relatedness was; not significant. There was no relationship between the changes in relatedness and changes in inbreeding. It is suggested that the sampling of queens from small discrete nests can influence subsequent estimates of relatedness. Worker relatedness was significant in all years in the non-polydomous population indicating that queens may be making unequal contributions to the worker population.