The effect of some organic solvents on interrupting diapause of Bombyx mori eggs was examined to provide a clue to the mechanism of diapause initiation. Methyl alcohol and benzene proved to be efficient in developing the prospective diapause eggs upto the stage of hatching or body pigmentation of the embryos. On the other hand, most of the eggs soaked in chloroform and mixture solution of chloroform-methyl alcohol (2:1) died in the early embryonic developmental stage with yellow or red brown colours, and the egg weights decreased upto ca. 40% of the original weight 8 days after the treatments. Methyl alcohol treatment for 2, 5 and 10 min to the 5hr-old-eggs led to empergence of the larvae, with high incidence (70∼80%) in the race of Kumchu X Chonghwa and with low indidence (1∼4%) in Daezo. The effect of same treatment to 20hr old eggs decreased to ca. 10% in the emergence of larvae in Kumchn X Chonghwa and increased to 20∼30% in Daezo, while the effect disappeared shortly after the diapause initiation (48hr-old-eggs). Considering the high dependency upon the egg age of the sensitivity to solvents, it was supposed that initiation and termination of diapause may be controlled by different mechanism. It was also suspected that the solvents exert their effect on the permeability of the eggshell.