Analysis of offsprings from mating of a Friend leukemia virus (FLV) resistant new mouse line, G, and DBA/S mice confirmed the existence of a single dominant gene for the resistance of G to FLV. In these offsprings, no correlation between resistance to FLV and hair-color genes (b, d and c) were observed. In the progeny of ((G X BALB/c) X DBA/2) mating, the resistance gene seregated independently from Fv-1. The allele(s) on Fv-1 locus in G mice seemed to be permissive to N-tropic virus. Therefore, conconmitance of Fv-1b in G mice was excluded. These results indicated that the resistance gene in the new line mice differ from Fv-1 and Fv-2.