Three groups of patients with pelvic endometriosis were treated with medroxyprogesterone acetate (MPA) 50 mg/day (n = 10), lynestrenol (LYN) 10 mg/day (n = 25) and danazol (DAN) 600 mg/day (n = 25) respectively. Total cholesterol, triglycerides, alpha-lipoprotein, prebetalipoprotein, beta-lipoprotein cholesterol, high-density (HDL) and low-density (LDL) lipoprotein and apolipoprotein A1 and B concentrations were determined before treatment and after 3 and 6 mth of therapy. Whereas lipid, lipoprotein and apolipoprotein levels did not change in the MPA group, the patients on LYN and in particular those on DNA showed marked changes in lipoportein patterns. Alpha-lipoprotein, HDL and apolipoprotein A1 levels fell, while beta-lipoprotein, LDL and apolipoprotein concentrations rose, these changes being statistically significant. No alterations were seen in the serum levels of cholesterol, triglycerides or prebetalipoprotein cholesterol. In view of a possible relationship between high LDL and low HDL levels and a risk of accelerated coronary arteriosclerosis in women it was concluded that progestogen-induced alterations in lipoprotein patterns should be avoided as far as long-term treatment is concerned and where additional risk factors are present.