Antigens obtained from adult female Setaria cervi were more protective than those of males against the development of microfilaremia in guinea pigs (transplanted with 10 S. cervi). In high dose levels (2 ml 500 microliters/ml) significant resistance was induced by antigens from male (52% of protection) and female (62% of protection) worms. The antigens from female worms were effective (40% protection) at low dose level (2 ml 50 microliters/ml) also.