A study on continuous low-dose estrone treatment achieved with two different silastic implants is presented. In the study estrogen treatment was supplemented with the addition of progestin in three different modes of application. The measurements of plasma estrone and estradiol concentration showed a 3- to 6-fold and a 2- to 3-fold increase, and that of FSH a decrease of 25%. The measurements of plasma estrone gave concentrations of 200-400 pg/ml and plasma estradiol was 70-200 pg/ml with uncovered estrone-releasing implants after 4 wk of treatment. The ratio of plasma levels of estrone/estradiol was around 3. The initial high estrone concentration after implantation could be eliminated by covering the rods with a thin layer of neutral silastic material. Plasma FSH and LH concentration significantly depressed when the estrone treatment was combined with levonorgestrel-releasing implants. The insertion of estrone-releasing implants alone and in combination with the cyclic treatment with norethindrone perorally, or with a norgestrienone-releasing silastic vaginal ring suppressed only the plasma FSH concentration. The climacteric complaints disappeared in a few days in every patient treated with uncovered estrone-releasing implants. Because it is easy to remove when required, the treatment with estrone-releasing silastic implants can be regarded as being safe for the patients.