Sodium selenite has been shown to inhibit Na, K-ATPase. Glutathione, at sufficient excess, is able to prevent or reverse the inhibition. Dithiothreitol can also reverse much of the inhibition, but KCN cannot. Selenomethionine does not inhibit Na, K-ATPase. The interactions of sodium selenite with Na, K-ATPase and glutathione may aid in understanding the early events in selenium cataractogenesis.