People who consume a diet rich in fruit and vegetables have lower risks of cancer, cardiovascular disease and all-cause mortality. Many prospective cohort studies have reported inverse associations between dietary intake or blood levels of beta-carotene and risks of cancer. Several large-scale trials were set up to assess whether beta-carotene supplementation might reduce the risk of cancer. Subsequently, evidence emerged from basic research which indicated that oxidative modification of low-density lipoprotein cholesterol increases its atherogenicity. The evidence from basic research, and epidemiological evidence for a possible protective effect of antioxidant vitamins for cardiovascular disease was strongest for vitamin E. More recently, further trials were set up to examine if supplementation with anti-oxidant vitamins might also reduce the risk of cardiovascular disease. This review summarises the available randomised evidence from published trials of beta-carotene supplementation involving 70,000 people from 3 large-scale trials in healthy populations and on vitamin E supplementation involving 29,000 patients at high-risk of cardiovascular disease from 5 large-scale trials. The results of these trials have been disappointing and failed to confirm any protective effect of these vitamins for either cancer or for cardiovascular disease.