Two pre-operative tests for the prediction of difficult intubation are assessed. A modified Mallampati test and a measurement of thyromental distance were performed at the pre-operative visit of 244 patients whose tracheas were subsequently intubated under general anaesthesia. Patients in whom the posterior pharyngeal wall could not be visualised below the soft palate, who also had a distance of less than 7 cm between the prominence of the thyroid cartilage and the bony point of the chin proved significantly more likely to present difficulty with intubation. The performance of these two simple tests on all patients before operation should allow the majority of cases of difficult intubation to be anticipated.