The question of the prevalence of the Sonne bacillus as the causative organism in outbreaks of diarrhóa in mental hospitals in this country was referred to the Infectious Diseases Sub-Committee by the Research and Clinical Committee of the Royal Medico-Psychological Association. At a meeting of the Sub-Committee the subject was discussed, and it was decided to send out a form, asking for information, to those mental hospitals which are engaged in active bacteriological work. Each hospital was asked to state whether any case of diarrhoea due to the Sonne bacillus had occurred during the past five years.