It is well known that pupils of diabetic patients are supersensitive to topical administration of autonomics, and whether the penetration of instilled drugs into the anterior chamber is high or not is an important problem from a causal point of view. Fluorescein penetration into the anterior chamber after topical instillation was examined by fluorophotometry in 39 diabetic patients aged 30-70 and 26 age-matched healthy subjects. Penetration increased in correlation with aging in both groups. Though there was no significant difference between the distribution of fluorescein penetration in patients with DR-Scott 0, I, II and those in healthy subjects, patients with DR-Scott III.V showed higher penetration than the former in each age-group. A study of the relation between the pupillary sensitivity to diluted solution of pilocarpine and fluorescein penetration in diabetic patients revealed significant correlation (r = 0.48, p less than 0.05) in cases aged less than 50. As a result, penetration of drug into the anterior chamber was considered to be a significant parameter of pupillary sensitivity.