1. Seven subjects were studied before and after the rate of cholesterol synthesis was altered with drugs or dietary cholesterol.
2. The rate at which plasma free cholesterol was formed from squalene during constant infusions of radioactive mevalonate increased with colestipol treatment, decreased with clofibrate treatment and decreased when cholesterol was added to the diet. The plasma squalene concentration showed corresponding changes, confirming that its measurement may qualitatively define changes in cholesterol synthesis.
3. The mean plasma squalene concentration in seven hypertriglyceridaemic, slightly overweight subjects was significantly higher than in six hypercholesterolaemic subjects, which is consistent with other evidence for increased cholesterol synthesis in hypertriglyceridaemia.