AIM: To assess the protective immunity engendered by anti-filaria-anti-idiotypic antibody (anti-fil-anti-Id-Ab) in jirds (Meriones unguiculatus) against Brugia malayi. METHODS: Anti-fil-anti-Id-Ab was prepared from rabbits immunized with anti-fil-IgG separated from high-titer sera from bancroftian filariasis patients with chyluria or hydrocele. Twenty two healthy jirds were randomly allocated to 3 groups. Group 1 (7 jirds) were each immunized with a single intrasplenic administration of anti-fil-anti-Id-IgG (4 jirds) or B. malayi soluble antigen (3 jirds). Group 2 (10 jirds) were each immunized with 3 repeated sc and ip administration of anti-fil-anti-Id-IgG (5 jirds) at 7-10-day intervals or B. malayi soluble antigen (5 jirds). Group 3 ( 5 jirds) served as challenge controls. Ten days after the last immunization, each jird in all three groups were challenged by ip route with 200 B. malayi third stage larvae. RESULTS: Jirds immunized with a single administration or 3 repeated administration of anti-fil-anti-Id-IgG could induce 50% and 80% protective immunity, respectively. No microfilaria or adult worms could be found in these jirds. In control group using rabbit anti-human IgG or B. malayi adult worm soluble antigen, no apparent protective immunity was found. CONCLUSION: Immunization of jirds with anti-fil-anti-Id-IgG resulted in protected immunity (50% - 80%) against B. malayi third stage larvae infection.