The ant species Lasius (Lasius) neglectus spec. nov. (van Loonet al., 1990) was sampled from its type locality in Budapest, Hungary for allozyme analysis at four marker loci. L. neglectus appeared to be monomorphic but different from L. alienus at three loci. The fourth locus, Me, was found to be polymorphic in L. neglectus and was used to make a preliminary assessment of population viscosity, intranest relatedness, and mating structure. Allele frequencies turned out to be homogeneous across motherqueens, males and workers. Between sample sites, the Me allele frequencies of workers were more heterogeneous and some population viscosity could be detected. The mean intranest relatedness of L. neglectus was found to be very low, both between workers and between workers and males, but no indications were found that queens are frequently inseminated more than once. The analysis of worker genotypes further showed a significant effect of inbreeding. The results are generally consistent with the observations about polygyny and intranidal mating reported by van Loonet al. (1990). Some striking similarities between L. neglectus and the Japanese L. sakagamii - the only other polygynous Lasius s.s. known to science - are discussed.