Hydroxylated metabolites of sulphadimidine, sulphamerazine, sulphatroxazole, sulphamethoxazole, and sulphadiazine exhibited antimicrobial activity againstEscheria coli28 PR 271 test strain ranging from 2.5 to 39.5 per cent of that of the parent drug. Trimethoprim addition potentiated the antimicrobial activity of these metabolites. N4‐acetyl sulphonamide metabolites possessed no antimicrobial activity, nor did trimethoprim potentiated them.