The problem of the relationship between the surface B antigen and the parasitosis characterized by active penetration of the larvae through the skin has not yet been resolved. Conflicting results have been reported lately on this problem even though it is currently believed that HBsAg is found more often among patients infected by parasites than among healthy subjects. Serum samples from 67 Somalian patients infected by S. haematobium were tested for the presence of the surface B antigen by ELISA method. The HBsAg was found in 19.4 per cent of these patients, while among controls (90 cases) the frequency of HBsAg was of 10 per cent. A comparative analysis of the results obtained with various methods in Somalia shows that the frequency of HBsAg among subjects with urinary schistosomiasis is of 25.9 per cent with indirect haemoagglutination (IHA), of 19.4 per cent with ELISA method and of 14.8 per cent with radioimmunoassay (RIA). These observations seem to indicate that the problem of an increased frequency of HBsAg among patients with urinary schistosomiasis needs further investigation.