Vitamin C (ascorbic acid) is an important anti-oxidant which may help to reduce free radical damage and atheroma formation in blood vessels. In a study in which a group of healthy volunteer subjects were followed up for 12 months and a group of patients with vascular disease taking Vitamin C supplements were followed for 23 months, we confirmed previous findings of seasonal variations in ascorbic acid and cholesterol and have shown an inverse relationship between leucocyte ascorbic acid and serum cholesterol levels. In healthy control subjects the increase in ascorbate and fall in cholesterol during the summer months was reversed when the weather changed to a more winter pattern, presumably due to dietary alterations. We found that ascorbic acid levels were lower in patients with peripheral vascular disease and that although normal ascorbic acid levels were achieved with Vitamin C supplementation, when supplements were stopped at the height of a normal summer, there was a fall in ascorbic acid and a rise in serum cholesterol to winter levels. Given these findings we suggest that patients with vascular disease should have Vitamin C supplements throughout the year.