In order to assess the effect of sex steroids on bone mineral density in Japanese with senile osteoporosis, the bone mineral density in 1/3 distal site of radius was measured serially before and after treatment for 2 years using single photon absorptiometry. Sixty seven old females with senile osteoporosis were divided into 4 groups, Group 1 (n = 28, mean age; 74.4 +/- 1.3 y.o., mean +/- SEM) was the control group, Group 2 (n = 14, mean age; 73.7 +/- 1.7 y.o.) was treated with 0.5-1.0 micrograms/day of 1 alpha -OHD3, Group 3 (n = 12, mean age; 75.4 +/- 2.9 y.o.) was treated with conjugated estrogen (Premarin) in a dose of 0.3125 mg/day (3 approximately 4 weeks administration followed by 1 week rest) and Group 4 (n = 13, mean age; 76.4 +/- 1.8 y.o.) was treated with sex-steroids (pregnenolone : androstenedione : androstenediol : testosterone : estrone = 1.0 mg : 1.0 mg : 0.5 mg : 0.1 mg : 5 micrograms/tablet) and thyroid hormone (thyroid-sicca 7.5 mg/tablet) preparation in a dose of 2 tablets/day. When the radial bone mineral density (RMD) before the treatment was taken as 100%, RMDs of each group at 6, 12, 18 and 24 months were 96.4 +/- 3.1%, 97.3 +/- 2.0%, 93.7 +/- 2.1% and 96.1 +/- 1.8% in Group 1, 100.8 +/- 2.8%, 106.4 +/- 2.1%, 101.3 +/- 3.4% and 108.8 +/- 2.9% in Group 2, 103.0 +/- 2.8%, 106.2 +/- 3.5%, 105.9 +/- 4.3% and 100.2 +/- 4.7% in Group 3, 105.3 +/- 2.2%, 104.7 +/- 2.3%, 112.6 +/- 6.4% and 112.1 +/- 6.7% in Group 4, respectively. Therefore, significant increases in RMD were observed in Groups 2, 3 (transient) and 4 when compared with Group 1. In Group 3, serum level of parathyroid hormone (PTH) was significantly (p less than 0.05) increased from 0.28 +/- 0.03 ng/ml before the treatment to 0.55 +/- 0.15 ng/ml at 24 months after the treatment. In Group 2, transient (6 months after the treatment) but significant (p less than 0.01) increase in urinary Ca/Creatinine ratio from 0.15 +/- 0.04 to 0.20 +/- 0.03 was found. Serum A1-P activities in Group 4 was shown to increase transiently from 131 +/- 10 IU to 151 +/- 12 IU (p less than 0.05) at 6 months and to 158 +/- 13 IU (p less than 0.01) at 12 months followed by subsequent decrease to 135 +/- 6 IU at 18 months and 133 +/- 10 IU at 24 months after the treatment.(ABSTRACT TRUNCATED AT 400 WORDS)