Peritoneal exudate cells (PEC) from normal jirds (Meriones unguiculatus) showed adherence of Brugia pahangi microfilariae, and subsequent cytotoxicity in the presence of antimicrofilarial antisera. Heat inactivation of the antisera diminished both adherence and cytotoxicity, but readdition of fresh normal jird sera only partially restored the reactions. Macrophages were the predominant adherent cell type. Circulating immune complexes precipitated with polyethylene glycol (PEG) from the sera of jirds with an 8-month infection inhibited both of these reactions. Complement consumption by the precipitated complexes was found not to be the cause of inhibition. Blocking of adherence and cytotoxicity by circulating immune complexes may be preventing the trapping of microfilariae in vivo, and may play a role in the persistence of microfilaraemia in the jird.