In a two-year period, 186 patients were admitted from Heathrow Airport to the nearest psychiatric hospital. Affective illness was related to time zone change. Depression was diagnosed significantly more often on flights from east to west (P less than 0.012 east to west versus west to east; P less than 0.015 north to south combined with south to north versus east to west, Fisher's exact probability test, two tailed). Hypomania was inversely related to depression in an east to west comparison (P less than 0.025). No other associations with direction of travel were seen in other diagnoses. Ninety-three (50 per cent) were diagnosed as schizophrenic; 24 of these had been aimlessly wandering. Twenty patients had been admitted at least once before under similar circumstances. Schizophrenic patients from Heathrow constituted 20 per cent of the total number of schizophrenic patients admitted to the hospital during that period.