It has been suggested that one of the mechanisms by which estrogen protects against postmenopausal osteoporosis is by modulating the production of cytokines, such as interleukin-1 (IL-1), tumor necrosis factors (TNF), and interleukin-6 (IL-6), in the bone microenvironment. In this study, reverse transcription/polymerase chain reaction (RT/PCR) was used to analyze expression of the mRNAs encoding these cytokines in freshly isolated human bone biopsy samples. Marked differences were found in the prevalence with which certain cytokines were expressed in different patient subgroups. Specifically, IL-1 alpha, IL-1 beta, and IL-6 mRNAs were expressed significantly more often in bone samples from postmenopausal women with osteoporotic fractures than in postmenopausal women with normal bone density or postmenopausal women on hormone replacement therapy (HRT). The prevalence of IL-1 alpha expression was 54% in bone samples from patients with osteoporotic fractures (n = 22), compared with 30% in nonosteoporotic postmenopausal patients (n = 10) and 10% in postmenopausal patients on HRT (difference between groups by chi 2 test = 7.0; DF = 2, p < 0.05). Corresponding figures for IL-1 beta were 54 versus 30 versus 0% (chi 2 = 8.6; DF = 2, p < 0.01) and, for IL-6, 94 versus 51 versus 40%; chi 2 = 13.5; DF = 2, p < 0.01). TNF-alpha was expressed in a similar proportion of osteoporotic (63%) and normal postmenopausal patients (60%), whereas only 10% of HRT-treated patients showed expression of TNF-alpha (chi 2 = 8.2; DF = 2, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)