Lenses incubated for 24 or 63 hours in media containing either lysophosphatidyl choline or phospholipase A gained Na+ ions and water. Electrolyte imbalances and damage to lens fiber membranes occurred at lysophosphatidyl choline and phospholipase A concentrations of 7.5 mug per milliliter and 0.25 mug per milliliter, respectively. Intravitreal injection of 250 mug of lysophosphatidyl choline or 0.4 mug of phospholipase A induced posterior subcapsular cataracts which progressed to maturity only in the latter instance. This is the first demonstration of the cataractogenic effects of a naturally occurring aqueous humor phospholipid or its generating enzyme.