An antigenic fraction has been isolated from adult worms of cattle fil
arial parasite Setaria digitata. The fraction exhibited high protease
activity against azocoll with optimum pH at 7.0. Elevated levels of an
tibodies to the protease were observed in asymptomatic microfilaraemic
individuals compared to the normal people of endemic regions. Such di
stinction was however not observed with the whole antigenic extracts o
f adult worms. The potential of the protease as immunodiagnostic antig
en is indicated.