Circulating antifilarial IgM and IgG antibodies were assessed by indirect ELISA in 184 serum specimens from 80 patients with clinically and parasitologically diagnosed filarial infections (20 with acute filariasis 40 with chronic filariasis & 20 asymptomatic microfilaraemic subjects), 64 individuals with other parasitic infections, 20 parasitologically-free subjects from filariasis endemic areas and 20 normal healthy controls. A soluble surface membrane extract from Dirofilaria immitis worms was used as the antigen. Using a single serum dilution of 1:128 and optical densities (OD) at 492 nm, the respective cut off values for IgM and IgG were found to be 0.24 and 0.22. All healthy non-endemic controls were seronegative by IgM and IgG ELISAs. The highest antifilarial IgM OD492 values were obtained in 20 patients with acute filariasis (95% sensitivity), while the highest antifilarial IgG OD492 values were observed n 40 patients with chronic filariaisis (97.5% sensitivity). Asymptomatic microfilaraemic subjects gave IgM and IgG OD492 values which were significantly lower than those of other forms of clinical disease and endemic control subjects. The antifilarial IgM and IgG respective sensitivities in asymptomatic subjects were 75% and 70%. Endemic controls had positive antifilarial IgM (65%) and IgG (75%) levels. Of 64 subjects with other parasites only one with Ancylostoma duodenale had positive IgM level (98.4% specificity); while 9 patients with nematodal infections mainly had false positive antifilarial IgG antibody levels (85.9% specificity). These results suggest that measuring circulating antifilarial IgM antibody level may have some diagnostic advantage over measuring IgG antibody level for the detection of active filarial infection and consequently better management of the disease.