We studied the effect of egg retention on the ability of mosquitoes to develop more eggs after a second blood meal. In Aedes sollicitans, the retention of 65 eggs prevented yolk deposition in the remaining undeveloped ultimate follicles, whereas in Aedes taeniorhynchus and Aedes aegypti the retention of 120 eggs was required for inhibition. When the latter 2 species retained 50–60 eggs, about 65 more eggs matured after the second meal but at a slower rate than after the first meal. When both ovaries were removed from A. sollicitans and one ovary was reimplanted, eggs matured in that denervated ovary after a blood meal. While these eggs were retained, yolk deposition was inhibited in follicles of an immature ovary transplanted before the second blood meal. Similarly, when either A. taeniorhynchus or A. aegypti retained 120 eggs in 2 denervated ovaries, yolk deposition in a transplanted immature ovary was inhibited after another blood meal. Furthermore, developing follicles in an intact or denervated ovary of A. sollicitans prevented yolk deposition in a third (transplanted) ovary in which the follicles were less developed. However, when the transplanted ovary was in an equal stage of development as the host, all 3 ovaries produced eggs. Apparently, during development the ovaries secrete a humoral factor that directly or indirectly inhibits yolk deposition in less developed follicles. This factor is present as long as eggs are retained, but it disappears soon after oviposition.