A complete study of the effects of drugs given before operation necessitates an investigation of the incidence and severity of postoperative emetic symptoms which might be attributable to their use. A method of such a study is described. The limitation of observations to patients anaesthetized with a standard anaesthetic technique for minor gynaecological operations reduces, as far as is clinically possible, the variable factors which could invalidate the findings. A scoring system for grading the severity of emetic signs and symptoms is described, and the importance of the choice of anaesthetic and the nature and duration of the operation is discussed.