The Og4C3 enzyme-linked immunosorbent assay (ELISA) to detect circulating Wuchereria bancrofti antigen uses 50 microL of serum. In this study, a whole blood sample absorbed on filter paper was tested as a substitute for serum. Serum samples were obtained from 60 Sri Lankan subjects by venepuncture and finger-prick blood samples from the same individuals were directly absorbed on filter paper. Og4C3 ELISAs using serum and filter paper blood were compared. Despite the fact that the estimated amount of serum available for the ELISA with filter paper blood was only one-fifth of that available when serum was used, the 2 ELISAs gave almost identical results. Of the 39 positive serum samples, 38 were detected using filter paper blood. Employing the ELISA using filter paper blood, 619 people in Matara, Sri Lanka, were examined for antigenaemia. The positivity rate was 22.5%, 3.1 times higher than the rate of microfilaraemia detected by examination of 60 microL blood films.