Corticosteroid-induced osteoporosis, which particularly affects the axial skeleton and the proximal femur, is characterized by a state of low bone remodelling. Fluoride is a potent stimulator of trabecular bone formation which could potentially be useful in the treatment of corticosteroid-induced osteoporosis. We investigated the effects of sodium monofluorophosphate (26 mg/day of fluoride) combined with 1000 mg of calcium (MFP-calcium-treated group), or of calcium alone (control), given for 18 months, on bone mineral density (BMD) of lumbar spine (LS), femoral neck (FN) and midfemoral shaft (FS) in 48 patients with corticosteroid-induced osteoporosis. Mean ages were 49.4 +/- 3.1 and 51.6 +/- 3.0 years (mean +/- SEM), duration of corticosteroid therapy 7.5 +/- 1.8 and 9.3 +/- 1.7 years, and mean daily dose of prednisone 18.2 +/- 2.3 and 12.1 +/- 1.1 mg in the MFP-calcium-treated group and controls, respectively. Initial BMDs (expressed as the Z-score, i.e. the difference in standard deviations from age- and sex-matched normal subjects) were -1.5 +/- 0.2 and -1.2 +/- 0.2 for LS, -1.4 +/- 0.2 and -1.3 +/- 0.2 for FN, and -0.8 +/- 0.3 and -0.6 +/- 0.3 for FS, in the MFP-calcium-treated group and controls, respectively. Analysis by linear regression of 6-monthly measurement values revealed BMD changes of +7.8 +/- 2.2 versus +3.6 +/- 1.3% (p < 0.02) for LS, -1.5 +/- 1.8 versus +0.9 +/- 1.8% for FN, and -1.1 +/- 1.1 versus -0.5 +/- 1.4% for FS after 18 months of follow-up in the MFP-calcium-treated group and controls, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)