Restriction fragment length polymorphisms from PCR amplified ribosomal DNAs of three Trichogramma species, T. minutum, T. brassicae, and T. near sibiricum, were studied. Length variation in the internal transcribed spacer (ITS) region was observed. The ITS region of T. brassicae is about 1350 base pairs (bp) in length and those of T. minutum and T. near sibiricum are 1300 bp. These three species also differ in the size of their ITS1 and ITS2 regions. Restriction enzyme digestions of these regions showed unique banding patterns for each species. The amplified 18S region of ribosomal DNA is about 1800 bp in length and showed no length variation between the three species of Trichogramma. Restriction enzyme digestion of this region by BamHI differentiated T. brassicae from the other two species. Restriction site maps of the ITS and 18S regions were constructed for each species. The amplified 28S region is about 1700 bp for these three species. Restriction of this region by RsaI and SacII differentiates these three species. The reported results indicate that these species of Trichogramma can be clearly differentiated from one another by nuclear ribosomal DNA markers.