The purposes of these experiments were to measure the influence of 14 trace elements on cataractogenesis and to test if these trace elements could prevent cataracts induced by selenium. On days 5-9 postpartum, suckling white rats received daily subcutaneous injections of either selenium (0.15 mumoles Se, as Na2SeO3, per pup) or selenium plus one of 14 other trace elements (separate subcutaneous injection) at one to five times the molar concentration of selenium. The frequency and severity of cataracts at three locations in the lens were assessed by slit-lamp examination on day 26-28 postpartum. Seven ions were found to be effective in preventing selenium-induced cataracts (% protection): mercuric (100%), silver (80%), cyanide (75%), arsenite (75%), cadmium (60%), and cupric (44%). Tellurite ion offered only 20% protection, while ferrous, zinc, lead, chromic, molybdate, tungstate, and vanadate ions provided no protection against selenium-induced cataract. No significant differences were found between the concentration of selenium in the lenses of control and cataractous lenses when measured approximately three weeks after selenium injection. Except for selenium, none of the trace minerals alone caused cataracts under our experimental conditions. In addition to subcutaneous injection of selenium, oral administration of this element was also found to cause cataract. It was concluded that among the ions studied, selenite was a powerful and rapid promoter of nuclear cataract formation, and that the protection ions may serve as useful probes for elucidating the mechanism of selenium-induced cataracts.