Nine diabetic patients (age range 23-67y) with autonomic neuropathy and symptomatic postural hypotension were studied. The time course of the postural drop in blood pressure (BP) was documented firstly at 0900h, prior to breakfast and insulin, and secondly in the afternoon. Seven patients were symptomatic in the morning but only one in the afternoon. The systolic nadir in the morning was lower (p less than 0.02) than in the afternoon. The mean systolic pressure in the first 3 min after standing was no different in the afternoon but it was lower in the 2nd (p less than 0.05), 3rd (p less than 0.02), and 4th (p less than 0.02) 3-min intervals in the afternoon. The time taken to reach the systolic nadir was variable, ranging from 1-12 min. It is concluded that the assessment of the postural fall in BP may be underestimated if measured immediately after standing or if it is measured in the afternoon.