Stable, nonradioactive tracer techniques have provided a safe means of studying in-vivo lipoprotein metabolism, and endogenous labelling with amino acids has allowed apolipoprotein synthesis to be analysed directly. Recent studies have dealt with experimental design, mass spectrometry techniques and the validity of simple formulae used to derive primary kinetic data. Concerns that stable isotopes give different results to the traditional radiolabelling studies have been allayed, in the case of apolipoprotein A-I, by published work. Studies conducted during the review period have also examined the mechanisms responsible for the low plasma concentrations of apolipoprotein A-I and apolipoprotein A-II in lecithin:cholesterol acyltransferase deficiency and the increased concentrations of HDL-apolipoprotein A-I caused by transdermal oestrogen hormone replacement therapy. The first analysis of lipoprotein-lipid rather than lipoprotein-apolipoprotein metabolism using stable isotopes has also been reported.