Restriction Fragment Length Polymorphism of Polymerase Chain Reaction products was used to differentiate species of Pteromalid wasp parasites of muscoid flies. Muscidifurax and Spalangia species can be easily distinguished as larvae, pupae and adults inside the host puparium or after emergence. Sequences from the nuclear rDNA intergenic transcribed space region 1, ITS- 1, and portions of the 28s gene were useful for examining the phylogenetic relationships among Muscidifurax and Spalangia species.