A delay in absorption of subretinal fluid after surgical repair for rhegmatogenous retinal detachment beyond 6 weeks was recognized in 39 of 575 consecutive cases undergoing scleral buckling procedures. The most common preoperative condition that was identified in these eyes was large clumps of cells on the undersurface of the detached retina. These cream-colored aggregates appeared similar to mutton-fat keratic precipitates and are referred to as subretinal precipitates. Most likely caused by aggregates of macrophages, they were present in 12 percent of the overall series of cases; subretinal precipitates also were recognized and documented before operation in nearly half of the eyes with delayed fluid absorption, a relationship that is highly significant in statistical analysis (P less than 0.001). On recognizing them before operation, the clinician can expect that approximately a fourth of the eyes will have fluid persisting beyond 6 weeks from the time of surgical repair until complete absorption. A second relatively common condition associated with delayed absorption of fluid that could be recognized in advance of surgical treatment was a long-standing peripheral (usually inferior) retinal detachment, which typically spared the macula, was associated with demarcation lines, and was caused by round atrophic holes with or without lattice degeneration. The presence of demarcation lines (reflecting relatively long-standing retinal detachment) was also positively correlated with delayed fluid absorption (P less than 0.02). Other conditions associated with delayed absorption of fluid included detachments of long-standing duration by history (especially when associated with previous unsuccessful efforts to repair the retina), vitreoretinal traction, and conditions whereby the choriocapillaris-retinal pigment epithelial complex and been significantly disturbed. Such conditions included hemorrhage into the subretinal space as a complication of surgical relase of subretinal fluid, previous retinal surgery, and possibly heavy treatment with cryopexy, especially when associated with exudative detachment. An analysis of subretinal fluide from 39 eyes showed a positive relationship between protein concentration and duration of the detachment but no relationship to a variety of other factors, including the presence of subretinal precipitates. Commonly identified cellular structures in the subretinal space consisted of pigmentladen macrophages. When studied by electron microscopy, some of these were thought to have originated from the retinal pigment epithelium.