Eleven Danish populations of the diploid Dactylorhiza incarnata s.lat. have been examined for allozyme variation in DIA, PGD, PGI, PGM, SKD, TP1, and UGPP. The results reveal a deficiency of heterozygotes in several populations. Possible reasons for this deficiency are considered. The results also indicate that no genetic barrier seems to prevent gene flow between D. incarnata var. incarnata, var. dunensis, and var. ochrantha — and some indication exists that a considerable amount of gene exchange takes place between sympatric populations of var. incarnata and var. ochrantha. On the other hand, there is no sign of recent introgression between D. incarnata s.lat. and any of the sympatric tetraploid species (D. maculata, D. majalis, D. purpurella s.lat.). It is suggested that knowledge on the various degrees of genetic integrity of morphologically recognizable entities should be elaborated and subsequently utilized for a biosystematic approach to Dactylorhiza.