Patency of Brugia malayi infection in gerbils born of infected parents was compared to that in gerbils from noninfected parents. Following infection with third stage larvae, female progeny of infected parents generally became microfilaremic whereas those of noninfected parents rarely did so. Male progeny developed microfilaremia regardless of parentage, although descendants of infected parents tended to have higher parasitemia. We conclude that B. malayi infection in the mother predisposes the offspring to patent infection subsequent to inoculation with infective larvae.