Analysis of high density lipoprotein (HDL) isolated from serum without major hypertriglyceridaemia and by five different precipitation methods showed that there were no significant differences in total cholesterol and triglyceride concentrations in the HDL supernatants prepared by the different methods but that free cholesterol, phospholipid, apolipoprotein (apo) A-I and HDL particles containing apo A-I but not apo A-II (LpAI) concentrations were significantly lower for heparin-manganese chloride method 2 (final manganese chloride concentration 92 mmol/l) compared with the other methods. Modest differences in HDL cholesterol, apo A-I and LpAI were observed between heparin-manganese chloride method 1 (final magnesium concentration 46 mmol/l) and the dextran sulphate, phosphotungstate and polyethylene glycol 6000 methods. Lipoprotein(a) (Lp(a)) and apo B were undetectable in the HDL supernatants, indicating that apo B-containing lipoproteins including Lp(a) were essentially completely removed by all the precipitation procedures.