Previous results have indicated that laboratory strains of yeast possessing two types of dsRNA virus-like particles, V1 and V2, are capable of producing a killer toxin which kills sensitive strains. This paper reports on genetic crosses which correlate the presence of these particles both with a host nuclear gene +/-/mak1 and with the production of a killer toxin. The results show that: (i) V1 particles are inherited independently of the +/-/mak1 gene. (ii) V2 particles are present only in combination with those of V1 and the +/- allele of the +/-/mak1 nuclear gene.