To illustrate whether a hemolysin in $delta$-endotoxins of Bacillus thuringiensis strain 73E10-2 and subsp. israelensis had immunological identity, a cyt gene of the strain 73E10-2 which encodes a hemolysin was cloned to B. subtilis (transformant 2753). The transformant 2753 containing cyt gene produced the hemolysin which lysed sheep erythrocytes after treatment of proteinase K. The hemolysin was proved also to be toxic against mosquito larvae (Aedes aegypti). The molecular weight of the hemolysin produced from the transformant 2753 was determined to be about 25 kDa by SDS-PAGE and immunoblot. The hemolysin in $delta$-endotoxin of subsp. israelensis and subsp. kyushensis did not react on immunoblot using polyclonal anti-$delta$-endotoxin of the strain 73E10-2, but 70-140 kDa mosquitocidal toxins in $delta$-endotoxin of subsp. kyushuensis reacted.