Sera from 1071 patients in nine age categories were screened for Toxoplasma antibody by indirect immunofluorescence. Thirty per cent of the sera contained antibody at a titre ≥ 1/16. The percentage of sera containing antibody rose from 3% in the 6 months–5 years age group to a maximum of about 40% in the 31–40 years age group. It remained constant thereafter. Eleven per cent of the 84 sera with Toxoplasma antibody titres ≥ 1/128 had Toxoplasma IgM titres ≥ 1/32. No significant difference was found in the possession of antibody between the sexes.