A double-blind randomized study was performed in 100 patients undergoing thyroidectomy to evaluate the effect of positive therapeutic suggestions made during neurolept-anaesthesia. The classic droperidol-fentanyl-N2O technique was used as these drugs preserve the neurophysiological functions required to process the information in the therapeutic suggestions given during general anaesthesia. Patients in the suggestion group heard positive non-affirmative suggestions during the whole operation. An autoreverse tape player was used. The control group listened to an empty tape. Both groups were comparable with respect to demographic variables, anaesthetic technique, drug dosage, duration of anaesthesia and surgery. Patients in the suggestion group suffered significantly less from post-operative nausea or volumiting (suggestion: 47.2% vs. control: 85.7%) and required less anti-emetic treatment (suggestion: 30.6% vs. control: 68.6%). We conclude that therapeutic suggestions heard during neurolept-anaesthesia are processed and decrease post-operative nausea and vomiting in patients after thyroidectomy.