Thiotepa (tris (1-aziridinyl) phosphine sulphide is known to be an effective pupal sterilant against Ae. aegypti. Studies were initiated to develop a method which could be adopted for sterile male releases. The present investigations have revealed that <99.6% sterility in males can be induced by immersing pupae to 0.6% thiotepa solution for 3 hr at 28+2C. Female sterility at this dose is only 42%. The sterilized males (36-60 hr old) were almost at competitive as normal laboratory males of the same age both in laboratory cages and in a field cage experiment. Two to 10% females showed double matings when females were offered 2 types simultaneously , however, when both types of males were offered in sequence, the frequency of double mating was lower. The number of females inseminated by sterile males was found to be slightly lower than for normal males. Thiotepa-induced sterility in males persisted for at least 17 days. The sperms once stored in the spermathecae of females mated with sterile males did not show any recovery of fertility during 3 gonotrophic cycles. Thiotepa did not induce inherited sterility or sex-linked recessive lethals in the progeny.