the effects of sex hormones on immune function a metaanalysis the effects of sex hormones on immune function have received much attention especially following the proposal of the immunocompetence handicap hypothesis many studies both experimental and correlational have been conducted to test the relationship between immune function and the sex hormones testosterone in males and oestrogen in females however the results are mixed we conducted four crossspecies metaanalyses to investigate the relationship between sex hormones and immune function i the effect of testosterone manipulation on immune function in males ii the correlation between circulating testosterone level and immune function in males iii the effect of oestrogen manipulation on immune function in females and iv the correlation between circulating oestrogen level and immune function in females the results from the experimental studies showed that testosterone had a mediumsized immunosuppressive effect on immune function the effect of oestrogen on the other hand depended on the immune measure used oestrogen suppressed cellmediated immune function while reducing parasite loads the overall correlation metaanalytic relationship between circulating sex hormone level and immune function was not statistically significant for either testosterone or oestrogen despite the power of metaanalysis these results suggest that correlational studies have limited value for testing the effects of sex hormones on immune function we found little evidence of publication bias in the four data sets using indirect tests there was a weak and positive relationship between year of publication and effect size for experimental studies of testosterone that became nonsignificant after we controlled for castration and immune measure suggesting that the temporal trend was due to changes in these moderators over time graphical analyses suggest that the temporal trend was due to an increased use of cytokine measures across time we found substantial heterogeneity in effect sizes except in correlational studies of testosterone even after we accounted for the relevant random and fixed factors in conclusion our results provide good evidence that testosterone suppresses immune function and that the effect of oestrogen varies depending on the immune measure used