A simple portable pupillometer using Polaroid photography has been developed for use in the diagnosis of diabetic autonomic neuropathy. The pupil diameter per cent (PD%), defined as the percentage of iris diameter to which pupil diameter had dilated in darkness, was measured from the instant colour prints. An age-related normal range was constructed from measurements in 163 healthy subjects in whom PD% declined linearly by 3% per decade. The PD% was measured in 15 patients with automatic neuropathy and 12 were identified with abnormally low values indicating a failure of sympathetically mediated dilatation. Results were consistent with the standard television pupillometric technique and had the same high repeatability with a coefficient of variation of 3.2%.