Org OD 14 is a synthetic steroid which in animal bioassays displays oestrogenic as well as very weak androgenic-anabolic properties. Earlier studies have shown that it alleviates oestrogen-deficiency symptoms and retards osteoporosis. OD 14 can be administered continuously with little effect on the endometrium. The aim of this study was to evaluate the effect of OD 14 on apolipoprotein A1 (Apo-A1), the major protein constituent of the high-density lipoprotein (HDL) fraction, as compared with that of oestradiol valerate (E2V) and a placebo. Twenty-two women, who had been oophorectomized when undergoing surgical treatment for stage IB or IIA cervical carcinoma, were given OD 14 2.5 mg/day, a placebo, and E2V 2 mg/day for a period of 6 wk in each case using a double-blind, cross-over method. Serum Apo-A1 was determined by electro-immunoassay after each treatment period. There was a marked decrease in Apo-A1 after OD 14 as compared with the levels seen after the placebo and E2V. This decrease is interpreted as evidence of a strong androgenic influence by OD 14. In epidemiological studies low levels of Apo-A1 have been associated with a higher incidence of atherosclerosis and cardiovascular disease. Long-term treatment with OD 14 might therefore be hazardous in this respect.