The concentration, composition and metabolic regulation of the free acid (FFA) pool in tissues other than the adipose are not well known. However, it has been reported that many cellular processes are affected by or are dependent upon the components of the FFA pool. FFAs, among other effects are potent uncouplers of the oxidative phosphorylation from the respirat0.v chain (for references see [ 1 and 21; they are necessary as precursors of prostaglandins [3,4] ; they may be involved in the onset of irreversible brain damage caused by ischemia [S, 61; they inhibit Na-K-dependent ATP-ase in brain [7] and they are inhibitors of key glycolytic enzymes (for references see [l] . Certain aspects of the intrinsic FFAs have been explored but only in a few tissues, e.g., in Ehrlich ascites tumor cells [S, 93 , human platelets [lo], cultured cells [ 1 l] and bran [ 1, 5, 6, 12, 131. Bovine retina neutral [ 141 and polar-lipids [ 151 are richly in long-chain polyenoic fatty acids. FFAs are a relatively small and labile pool, also composed of a large proportion of polyunsaturated constituents. This letter reports remarkable features of endogenously produced retina FFAs, showing that they arise from membrane lipids, and that a different behavior is apparent in the rate of release of individual FFA from the tissue in vitro. The present data may be of