The compositions of the four madia and their pHs for delta endotoxin production by B. thuringiensis serovar kurstaki 3a3b were examined. In the M-4 media out of the 4 media at pH8, the production of the endotoxin and spore formation were maximal. The mean generation times of the bacterium were 53.4 minutes in the M-1 media, 98 in the M-2, 132 in the M-3, and 127.5 in the M-4. The proper pHs of the media for the endotoxin production appeared to be pH 7 to 8. In the M-4 media, the lag time lasted about 5 hours.