The pupil cycle time (PCT) was prolonged in 11 subjects with familial dysautonomia. In the younger age group (10-19 years), mean PCT was 872 +/- 88 msec as compared to 15 normal age matched controls (728 +/- 88). In the 3 oldest patients (30-39 years) mean PCT was 980 +/- 133 msec as compared to 13 age matched normals (748 +/- 56). It is proposed that prolongation of PCT in familial dysautonomia may be due to functional denervation of the iris or that it is a result of a structural abnormality of its musculature and/or its neuromuscular junctions.