Cycling populations ofA. aegypti of wild origin were established in outdoor cages. Releases were then made for 32–43 days of either males carrying chromosome translocations or males of the sex ratio distorter type. The translocation caused a maximum of 50% sterility, but this declined rapidly after termination of releases. The distorter males depressed the proportion of females among the pupae produced in the cage to a minimum of 35% and the distortion of sex ratio persisted for 13 weeks following termination of releases. It was pos sible to simulate the effects of the releases with a computer. Simulations were also made of standard release schedules of three types of genetic material. A strain carrying both sex ratio distortion and a translocation gave the most effective population suppression.