The effects of various numbers of Toxorhynchites rutilus larvae were tested on more or less stable populations of Aedes aegypti larvae in artificial containers. Pupation time for the predator was dependent on the number of prey available during the larval stage. Cannibalism did not appear to be a major problem, even when different-sized predators were present in the same container. Weekly introduction of a predator larva to each container gave better overall control of Ae. aegypti than did a single initial introduction of one or 2 larvae per container.