Anisocoria in darkness and during reflex responses to unilateral light stimulation was studied in 150 normal subjects with television pupillometry. It was commonly found that the direct light reaction of the stimulation eye exceeded the consensual reaction of the other eye. This light-induced anisocoria, termed 'contraction anisocoria', had a mean value of 0.075 mm or 6.1 % of light reflex amplitude. The measurement showed a high degree of repeatability in 20 subjects who were tested on two occasions a year apart. It occurred in the presence and absence of prior dark adaptation and increased proportionally with reflex amplitude as the intensity of the stimulating light was raised. IT IS CONCLUDED THAT, CONTRARY TO PREVIOUS OPINION, A SMALL DEGREE OF CONTRACTION ANISOCORIA IS NORMAL.