Fifteen patients with hyperlipoproteinemia (HLP), types IIA (n = 8), IIB (n = 3) and IV (n = 4) were given 40 g of heat prepared alfalfa seeds 3 times daily at mealtimes for 8 weeks with otherwise unchanged diet. In patients with type II HLP alfalfa treatment caused after 8 weeks a maximal lowering of pretreatment median values of total plasma cholesterol from 9.58 to 8.00 mmol/l (P less than 0.001) and low density lipoprotein (LDL) cholesterol from 7.69 to 6.33 mmol/l (P less than 0.01), which corresponds to decreases of 17% and 18%, respectively. Maximal decrease was 26% in total cholesterol and 30% in LDL cholesterol. In two patients with hypercholesterolemia the LDL cholesterol decreased less than 5%. Apolipoprotein B decreased in the same period from 2.17 to 1.43 g/l (P less than 0.05) in type II HLP, corresponding to 34% decrease, whereas apolipoprotein A-I did not change. Body weight increased slightly during the first 4 weeks of alfalfa treatment (P less than 0.001) probably because of the caloric content in the alfalfa seeds. After cessation of treatment, all lipoprotein concentrations returned to pretreatment levels. We conclude that alfalfa seeds can be added to the diet to help normalize serum cholesterol concentrations in patients with type II HLP.