Biochemical analyses of subretinal fluid revealed a consistently high ascorbate level in the subretinal fluid of patients with rhegmatogenous retinal detachment. The average values and SDs of ascorbate in anterior chamber aqueous humor, subretinal fluid, and blood were 14.7 +/- 1.8, 27.4 +/- 2.1, and 1.8 +/- 0.2 mg/dL, respectively. The ascorbate concentration in subretinal fluid was always higher than that in aqueous humor. The high ascorbate level in subretinal fluid led to the hypothesis that aqueous humor contributes to the formation of subretinal fluid. Presumably and constant absorption of subretinal fluid by the choroid directs a portion of the aqueous humor from the posterior chamber into the subretinal space. The posterior movement of aqueous humor causes reduced ascorbate concentration in the anterior chamber and relative hypotony of eyes with rhegmatogenous retinal detachment. Closing the retinal break results in an interruption of the posterior movement of aqueous humor and rapid absorption of the remaining subretinal fluid by the choroid.