Genetic polymorphism of the two Palaearctic sulphur butterflies Colias crocea Fourc. and Colias erate Esp. was examined in serial samples using RAPD-PCR analysis of total cellular DNA. The primers OPA-01, OPA-03, OPA-04, OPA-08 were used. Taxon-specific molecular markers have been found for each species (markers OPA-08250, OPA-08380 were associated with rounded valve margin; marker OPA-04400 was associated with angled valve margin). The genetic diversity of C. erate is considerably less than that of C. crocea. Genetic evidence for interspecific hybridization between C. crocea and C. erate is presented. Interspecific hybrids in question (paratypical forms such as f. chlorodona and f. pseudochrysodona) are situated at intermediate position with regard to the parental species on dendrograms (UPGMA) and maximal spanning trees (MST). Completely additional RAPD-spectra were not obtained though taxonomic status of these paratypical forms stay still vague. Only f. eratoides has DNA markers that are absent in spectra of other specimens tested. Probably it is a cryptic species unrevealed by common morphological and biochemical methods and its investigation by the methods of molecular genetics (sequence of cloned DNA) is very desirable
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