Total substitution of soyabean protein for animal protein in the diet has been repeatedly shown to lower plasma cholesterol levels in hypercholesterolaemic individuals. A new, highly palatable, high-protein soya drink may allow replacement of a significant percentage of animal protein in the diet. The soya drink was given, within a crossover design v. a cows' milk preparation of similar composition and taste, to twenty-one severely hypercholesterolaemic patients (mean baseline plasma cholesterol 8·74 mmol/l) with a history of resistance to or intolerance of statin treatment. Each dietary supplement was given for 4 weeks, with a 4-week interval between treatments, Plasma lipid levels were monitored every 2 weeks during each dietary sequence. The concomitant dietary treatment, which had been followed for a long time by all patients, was carefully monitored throughout the study. The soya supplementation reduced plasma total cholesterol level by 6·5%, when given first, and by 7·4% when given after cows' milk. When given first, cows' milk resulted in a small, non-significant reduction of plasma cholesterol level (-3·9%), and when given after soya, it changed total plasma cholesterol to a minimal extent (-1·6%). Changes in total and LDL-cholesterol levels after 2 and 4 weeks of soya v. cows' milk treatment were, thus, respectively -6·1, -7·0 and -6·2, -7·8% (both P < 0·05). These first data from a double-blind study confirm a significant cholesterol-lowering effect of soyabean protein, even when only partly replacing animal protein in the diet, in individuals with extreme plasma cholesterol elevations.