Using immunoassay and immunoblotting approaches, antibodies to Sj26, a glutathione S-transferase molecule (Mr = 26,000) of Schistosoma japonicum worms that is a vaccine candidate, have been sought in three large human serum banks. For these studies, a near-native recombinant Sj26 molecule produced in Escherichia coli was used, generally in ELISAs. Anti-Sj26 activity was detected readily in a high proportion of the sera at titres below 1:400 and appeared to be largely protein A-binding IgG antibodies. No differences in the prevalence of anti-Sj26 antibodies were noted in sera from entirely normal individuals or those with a variety of parasitic infections, but never exposed to S. japonicum. The stimulus responsible for induction of these low titre, probably low affinity antibodies in humans remains unknown.