OBJECTIVE: We have previously demonstrated that exogenous progesterone, but not oestrogen, upregulated lymphocyte beta 2-adrenoceptors (beta 2-AR) when given during the follicular phase in healthy females. In the present study, we were interested to see whether this facilitatory effect of female sex-steroid hormones could be demonstrated in healthy males. METHODS: Nine healthy male volunteers with a mean age of 24 years completed this randomised, double-blind, placebo-controlled, cross-over study. They were randomised to receive either oral placebo, oestradiol valerate (4 mg) or medroxyprogesterone (40 mg). The study medication was given in two divided doses 12 h apart. Subjects attended the laboratory at baseline (T0 is baseline), 1 h after ingestion of the second dose of study medication (T1) and 24 h later (T24). At each visit, 60 ml of peripheral blood was withdrawn for measurement of serum oestradiol, progesterone and testosterone levels, and for lymphocyte beta 2-AR parameters; density (Bmax), binding affinity (Kd) and maximal cyclic AMP response to isoprenaline (Emax). RESULTS: Baseline levels of sex-steroid hormones were comparable for each of the treatment periods. Serum oestradiol levels increased significantly, twofold, 1 h after ingestion of oestradiol but there was no significant change in levels of serum progesterone and testosterone. Lymphocyte beta 2-AR parameters following treatment with oestradiol and progesterone did not change significantly from baseline and were not different from placebo. CONCLUSION: In contrast to previously reported effects in women, female sex-steroid hormones did not appear to have any significant facilitatory effects on lymphocyte beta 2-AR parameters when given exogenously to healthy males. This lack of effect may be due either to the absence of receptors for female sex hormones in beta 2-AR or to reduced efficacy of female hormone-receptor coupling in male lymphocytes.