Disparlure, (cis-7,8-epoxy-2-methyloctadecane) the sex attractant of the gypsy moth, Porthetria (Lymantria) dispar, attracts the male nun moth, Lymantria monacha, in the field and is a highly effective olfactory stimulus in electroantennogram (EAG) and single-cell recordings. We have now analyzed the extract of 2000 abdominal tips of the female nun moth. Physical and chemical tests, which included gas-chromatographic retention times, elution volumes from silica gel and silica gel-silver nitrate columns, mass spectra, epoxide functionality, EAG-activity of chromatographic fractions with gypsy moth antennae, presence of disparlure precursor, all indicated that disparlure is present in the extract of nun moth sex glands. The optical activity of the natural disparlure of the two species has not yet been determined. Several authors have reported 1-0 that disparlure,