Technical Abstract: The following technical abstract refers to a poster presentation given at the 2001 Annual Meeting of the Entomological Society of America. Mitochondrial, 18s ribosomal and Intergenic Transcribed Spacer 1 (ITS-1) sequences were used to develop diagnostic markers and examine the phylogenies of wasps parasitising house flies and stable flies. Mitochondrial sequences failed to differentiate M. raptorellus and M. uniraptor. Despite repeated attempts, we were unable to amplify CO-1 or CO-2 sequences from Spalangia species. Nuclear 18s ribosomal sequences were obtained for 4 species of Muscidifurax, 2 species of Spalangia, Trichomalopsis sarcophagae and Urolepis rufipes. Little variation was observed in the 630 base pair amplicon among the wasps with differentiation among species varying from 0 to 4%. Muscidifurax zaraptor and M. raptor had identical sequences, as did M. raptorellus and M. uniraptor. The other species were easily differentiated based upon this sequence. ITS-1 sequences were obtained for all of the above wasp species. The 4 species of Muscidifurax could be easily differentiated. Trichomalopsis sarcophagae and Urolepis rufipes sequences were similar to the Muscidifurax sequences. Spalangia sequences were very different from the Muscidifurax sequences to the point were alignment was not possible. Variation within the Spalangia was also very high with several regions where alignments were not possible.