Overproduction of very low-density lipoprotein apolipoprotein B by the liver is a metabolic marker for familial combined hyperlipidaemia, a common inherited disorder of lipoprotein metabolism. Four subjects with familial combined hyperlipidaemia had rates of apolipoprotein B production which were 2-7 times normal, using a protocol in which [15N]glycine was used to label newly synthesized hepatic proteins. Following 4-6 months of therapy with lovastatin, very low-density lipoprotein apolipoprotein B production in all four subjects had returned to the normal range. This demonstrates that lovastatin, an inhibitor of cholesterol biosynthesis, acts also to reduce the apparent production rate of apolipoprotein B by the liver.