The distribution of G1m(f,z,a, and x), G2m(n), G3m(b0, b1, b3, b5, c3, c5, g, s, t, and v), A2m(1 and 2) and Km(1) (formerly Inv[1]) allotypic determinants has been examined in a series of Czechoslovakian blood donors. The results indicate that Gmza;-;gvA2m1, Gmzax;-;gvA2m1, Gmf;n;bvA2m1 and Gmf;-;bvA2m1 are present in polymorphic frequencies. Further, 9 idiomorphic phenotypes were observed; however, without family data it was not possible to exactly define the majority of these. The observed frequencies of Gmza;g, Gmzax;g and Gmf;b and Km1 are similar to those observed previously in Czechoslovakians and similar to those observed in adjacent populations, though different from those observed in Western Europeans, primarily due to a higher frequency of Gmf;b in Czechoslovakians.