Reproductive capacity and activity patterns of native screwworm (Cochliomyia hominivorax(Coquerel)) males were evaluated by release and recapture of sterile females in central Belize. On six occasions 4,000 virgin, 1-d-old sterile females were released at a central location. A total of 382 sterile females and 66 native females were recaptured on sentinel sheep at four locations. Ratios of virgin to mated recaptured females were used to calculate an estimated number of matings per release. During the 65-d period of the test, numbers of recaptured females and mating percentages increased, then decreased for the last release. Location of sentinel animals, day after release, and individual releases were significant factors explaining capture rates for mated and nonmated released females and captures of native females. Mating capacity for the native population of screwworm males over the 10-d recapture period was estimated to range from 70 to 1,735 matings for the dispersal area of these females. These data and estimates suggest that although screwworm males have relatively low population densities, they have significant excess mating capacity, and that production and release of competitive sterile males is important for the success of the screwworm eradication program.