Fourth stage larvae of Aedes aegypti were exposed (24-48 hr) to 4 concentrations (0.005-0.05 uCi/ml) of 32P into their eggs in sufficient quantities so that individual eggs were identifiable with a gas-flow proportional counter. The average radiolabeled egg contained about 0.4% of the radioactivity measured in the female after oviposition. Females retained 65% of their radioactivity after 2 days of radioactive decay and oviposition of the first batch of eggs. They retained 34% of their radioactivity after 6 days of radioactive decay and the oviposition of 2 egg batches. The females from the 32P treatments produced about the same number of eggs as the control but the hatch was lower in eggs from the treated females. Eggs from the second oviposition had 59% of the radioactivity of eggs in the first oviposition. Eggs containing about 60 counts/min were easily separated from eggs laid by nonradioactive females when deposited together on the same oviposition substrate.