Circulating antigens, antibodies to somatic and sheath components of microfilariae (mf) and immune complexes were determined in parallel in different categories of Wuchereia bancrofti infection using, respectively, reverse indirect haemagglutination (RIHA), indirect haemagglutination (IHA), indirect immunofluorescent (IFA) and polyethylene glycol (PEG) precipitation assays. Rabbit hyperimmune anti-W. bancrofti mf serum and mf homogenates were used as reagents. Appreciable levels of antigens and antibodies were detected in all categories; endemic normals, asymptomatic carriers, acute and chronic filarial cases. For example, even amongst endemic normals, i.e. those with neither clinical nor parasitological evidence of infection, 66%, 71% and 74% had mf antigens, anti-mf antibodies and anti-sheath antibodies, respectively. Notably, only a small proportion (9.4%) of microfilaraemic individuals had detectable level of anti-sheath antibodies. The relationship of these parameters with the spectrum of filariasis is discussed.