In vivo experiments with rabbits show accelerated appearance of naphthalene-cataract after subconjunctival injection of pilocarplne. In vitro experiments stated that in lenses which were incubated for 24 h in a medium with pilo-carpine the phosphate content, especially the energetic phosphates were changed. Similar variations are found with other experimental damages of metabolism. It is yet unknown if the decrease of G6PDH [glucose-6-phosphodehydrogenase] activity caused by pilocarpine is related to the above-mentioned damages. This enzyme-activity is reduced considerably by addition of pilocarpine, the reaction which produces TPNH [triphosphopyridine nucleotide] is stopped and even reversed. This effect depends on pilocarpine concentration and can be eliminated under certain conditions by further addition of TPN [triphosphopyrtmidine nucleotide]. A longer period of pilocarpine influence prevents production of TPNH by further addition of TPN. The mechanism of the reaction is not yet elucidated.