Field tests were conducted in sparsely infested areas of Massachusetts to evaluate the effectiveness of microdispersable formulations of racemic disparlure in disrupting mating of Lymantria dispar (L.). The incidence of mating of laboratory-reared female moths placed in treated plots was significantly less than that in control plots, and the degree of mating disruption was correlated with the amount of disparlure applied. The number of male moths captured in (+)-disparlure-baited traps was also correlated with the incidence of mating. In plots treated with 50 g/ha, only 2% mating was observed, compared with 65% mating in control plots.