One hundred and seventy two strains of Clostridium difficile isolated from 62 patients with antibiotic associated diarrhoea or pseudomembranous colitis were analysed for the production of toxins A and B and typed using 35S-methionine labelling followed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). There was a correlation between production of toxins A and B and the type of C difficile. One hundred and forty four of 172 strains were either high or low producers of both toxins. Toxins were not detected in 28 of 172 strains. Types A and Y were consistently non-toxin producers; types B and E were high toxin producers. Type X, the epidemic strain, showed variable toxin production. Symptoms of 49 patients with haematological malignant pathology who were part of a documented outbreak of antibiotic associated diarrhoea, were analysed in relation to toxin production and type of the clinical strains isolated. In general, there was a correlation between symptoms of antibiotic associated diarrhoea, the type of C difficile, and its potential for producing toxins.