The aim of this study was to investigate the interactive effects between nutritional calcium (Ca) intake and hormone replacement therapy (HRT) on bone loss. The study population, 937 peri- and postmenopausal women, was selected from a random sample (n = 2025) of the OSTPRE-study cohort (n = 13,100) in Kuopio, Finland. Of them, 545 women had never used HRT and 392 women reported its use during the follow-up period of 6 years. Women were divided in groups according to self-reported daily nutritional Ca intake (mg/day): 927 (3rd). Bone mineral density of the lumbar spine and femoral neck was measured with dual X-ray absorptiometry at baseline in 1989-91 and at the 5-year follow-up in 1994-97. According to analysis of variance, there were no statistically significant differences in annual bone loss rate between Ca intake tertiles in HRT never users. In HRT users the annual bone loss at the femoral neck was significantly lower in the third tertile than in the second and first tertiles. In a linear regression model, Ca intake prevented femoral bone loss in HRT users (P