The pteromalid waspMuscidifurax zaraptorKogan&Legner, a solitary pupal parasite of house flies and stable flies, was released in May adjacent to three populations of freeze-killed house fly pupae. Additional populations of freeze killed pupae were placed 5, 10, and 15 m from the three release locations in the four cardinal directions. After 4 wk, levels of parasitism ranged from 40 to 49% 15 m from the release point at all three locations. Hosts placed out 2 wk after the parasites were placed in the field were heavily parasitized after 1 wk of exposure, suggesting that parasites were still moving from the release point or that the parasites were remaining at the sites of host exposure. Hosts placed out 4 wk after the releases had lower levels of parasitism than those exposed in weeks 0 and 2; this suggests that some of the parasites had left the area or had died. High levels of parasitism in hosts placed out in week 6 were attributed to parasitism by progeny of parasites initially released. The study suggests thatM. zaraptorreadily searches at least 15 m from a release point and parasitizes available hosts when encountered, and that when released in the center of a pen, movement away from release point is essentially uniform, at least over short distances.