In stables in El Salvador, Central America, 12.7% more adult Anopheles albimanus Wiedemann were captured during the early morning than during the evening. Also, oviposition from the morning-collected females was 57.4 greater than from those collected in the evening. There was no apparent difference either in the natural fertility of the 2 collections or in the sterility induced by a sterile-male release experiment. Logistical problems involving personnel work schedules and use of vehicles were eliminated by the early morning collections.