Isozyme variation was studied in a Helianthus argophgllus population, two inbred lines of sunflower, H. annuus, an interspecific line, and within progenies of crosses between those materials. Nine isozyme systems were resolved on starch gels. Fifteen loci were studied, I I of them being poly,rnor phic. Both species shared alleles at a_ll loci; four alleles were present only in H. argophylltts. Intrapopulation variability in the wild species was analyzed, and genetic distance among materials resembled their origin and genetic relationships. Isozj,'rne markers allowed evaluation of uniformity within inbred lines and identification of hybrid seed among progenies of all crosses.