The acute changes in intraocular pressure during sustained handgrip contraction (2.5 minutes duration) and the Valsalva manoeuvre (15 seconds duration), both standard tests of autonomic nerve function were studied in 14 diabetic patients and 14 similar aged control subjects. During sustained handgrip contraction, diastolic blood pressure increased by 16.35 +/- 1.87 mmHg in the diabetic patients and 21.36 +/- 0.66 mmHg for the control group. Mean intraocular pressure decreased by 0.71 +/- 0.43 mmHg in the diabetics, p less than 0.05 and 0.64 +/- 0.27 mmHg, p less than 0.01) in the control group. There was no correlation between the blood pressure and the intraocular pressure responses in either group. On release of handgrip contraction, mean recovery intraocular pressure over 5 minutes was significantly lower than mean baseline values for the two groups; control: baseline 14.78 +/- 0.49 to 14.14 +/- 0.67, p less than 0.001 and diabetic: 14.57 +/- 0.65 to 13.86 +/- 0.72, p less than 0.001. During the Valsalva manoeuvre, there was a significant rise in intraocular pressure in the control (+7.85 +/- 0.75 mmHg, p less than 0.001) and the diabetic group (+7.93 +/- 1.18 mmHg, p less than 0.001). 5 minutes after release of intrathoracic pressure, mean recovery intraocular pressure remained significantly below baseline values for the two groups. The Valsalva ratios were in the normal range for the control group (1.21 to 2.2) while 2 diabetics had abnormal ratios.