Genetic resistance of the silkworm to the flacherie-virus infection was studied using several Japanese and Chinese races as well as their hybrids. The results obtained are summarized as follows:
1. Resistance to the viral infection is a recessive genetic character which is probably controlled by a major gene.
2. Hybrid vigor or heterosis in the resistance could not be entirely observed among the tested hybrids.
3. It was also found that the selection of a resistant strain could be readily accomplished by the batch selection method for several generations.