Fifty-five analogues of disparlure, the sex attractant of Porthetria dispar (L.), were synthesized and tested at 2 levels of concentration in the field vs. disparlure for attraction of male gypsy moths. Most of the analogues were ineffective; the best of these, which were 40- to 100-fold less active than disparlure, were those most closely related to disparlure in structure. The data may aid in deciphering the mechanism of odor reception.