The genome project of the nematode Caenorhabditis elegans is completed. It is important and useful to disrupt nematode genes to know their function. We treated wild-type animals with potential candidates for mutagens for reverse genetics, EMS (ethyl methanesulfonate), short-wavelength UV, and long-wavelength UV in the presence of TMP (trimethylpsoralen). We estimated forward mutation rates by counting the occurrence of a marker unc-22 mutation. me found that the forward mutation rate by TMP/UV could be comparable with EMS by improving the frequency one order higher than before. We next isolated mutants of another marker gene ben-1 and examined the probability for the deletion mutations by PCR and sequencing. Deletion mutations were found only by TMP/UV method, which suggested TMP/UV is the choice for deletion mutagenesis among these methods. As a pilot experiment, we could isolate actual deletion mutations at a much higher frequency than previously.