Interleukin-1 is a cytokine with bone-resorbing activity which is claimed to play a role in the pathogenesis of osteoporosis and of post-oophorectomy bone loss. We measured plasma levels of interleukin-1 (IL-1) in 16 women who underwent hysterectomy and bilateral oophorectomy and in 12 women with hysterectomy alone before surgery and 7, 15, 30, 45 and 60 days after surgery. Only oophorectomized patients showed a significant increase of circulating interleukin-1 levels. This increase was significant only 30 days after surgery, whereas a rise at 7 days (P < 0.001) was observed for serum calcium and hydroxyproline/creatinine and calcium/creatinine ratios. These data do not indicate a definite role of IL-1 in promoting bone resorption in estrogen-deficient women in vivo.