Evidence from epidemiological, in vitro and animal studies has accumulated to support the idea that aspirin, ibuprofen and paracetamol protect against cataract. In this study rats made diabetic with streptozotocin were given these drugs in their drinking solution for up to 160 days. All three drugs delayed cataract formation assessed by slit-lamp examination for a large part of this time. Blood glucose levels were a little lower in diabetic rats treated with aspirin and ibuprofen than in untreated diabetic rats although all groups remained diabetic. Similarly, the increased glycation (non-enzymic glycosylation) of lens proteins caused by diabetes was less in the diabetic rats treated with aspirin and ibuprofen. The fall in glutathione induced by diabetes was also alleviated by aspirin and ibuprofen. Paracetamol appeared to afford similar protection against the biochemical changes but its effect was not statistically significant. The decrease in glutathione and increase in glycation were related to the progression of lens opacification. The greatest loss of glutathione occurred at an early stage, whereas glycation had its greatest change at the later stages--nuclear and mature cataract. These results encourage the view that ibuprofen, aspirin and paracetamol could protect against cataract in man: a hypothesis that could be tested in a properly-conducted clinical trial.