Lysophosphatidyl choline (LPC), which has been shown to be toxic to the lens in organ culture, is markedly elevated in uveitic eyes. These findings have led to the suggestion that LPC is an initiator of cataractogenesis in uveitis. We report here that a factor not considered by previous investigators, i.e. the presence of serum proteins, can modulate LPC toxicity in vitro. First, the toxicity of LPC to lens epithelial cells or to whole lens in organ culture was effectively neutralized by addition of serum or serum albumin to the test cultures, thus suggesting that the potential toxicity of the increased LPC in the uveitic eye might be neutralized by the concomitant increase in serum protein. Secondly, the susceptibility to LPC toxicity of lens epithelial cells was no greater than that of lymphocytes which are normally exposed to LPC levels higher than those in the uveitic eye.