The ability of glaucomatous eyes to adjust to a sudden increase in intraocular pressure was investigated in nine certain glaucoma cases and in ten normal subjects. The "dynamic provoked circulatory response" (DPCR) was determined by continuously measuring the brightness of the papilla before (baseline), during, and after an abrupt artificial elevation in intraocular pressure. Following the onset of intraocular pressure elevation, the period during which the baseline brightness of the papilla persisted (latency time) was significantly (P less than 0.001) shorter in glaucomatous eyes (0.64 +/- 0.25 s) than in normal eyes (2.39 +/- 0.68 s). This led to the suggestion that the extent to which an eye can adjust to abruptly higher intraocular pressure is measurably reduced in glaucoma. That this effect can be quantified indicates a potentially useful method for detection and follow-up of glaucoma.