The exposure of female inbred virgin C3H/St mice infected with the Bittner particle to a commercial brand of beer increases body weight but has no significant effects on survival, the incidence of spontaneous mammary adenocarcinoma, tumor latency, or growth even on continuous administration of beer in place of drinking water over the entire postweaning lifespan of the animals. Prolactin excretion in young beer-group mice was slightly elevated but not significantly different from the prolactin levels observed in normally maintained control animals.