1. Pulse-wave velocity in both upper and lower limbs has been measured in a series of diabetic and control subjects. Subjects were studied with a Doppler ultrasound system and a real-time frequency analyser. 2. The subjects comprised three groups: (a) diabetic subjects with peripheral neuropathy (43); (b) non-complicated diabetic subjects (8); (c) non-diabetic control subjects (11). Those diabetic subjects with peripheral neuropathy included 12 with non-infected foot ulcers, nine with healed foot ulcers and 22 who gave no history of foot ulceration. All of the diabetic and control subjects had clinically normal peripheral pulses. 3. In the upper limbs the pulse-wave velocity was similar for all groups. By contrast, in the lower limbs pulse-wave velocity was significantly increased (P less than 0.005) in patients with healed or ulcerated feet compared with controls, non-complicated diabetic subjects or diabetic subjects with peripheral neuropathy alone. 4. It is suggested that the increased pulse-wave velocity results from an underlying, diffuse, atherosclerosis. This is not detectable clinically and was found to predominantly affect the lower limb arteries rather than the upper limb vessels. This may be an important aetiological factor in the development of foot ulcers in these patients.