Russell N, et al. - The effects of 2 low doses of daily transdermal estradiol (E2) gel on circulating E2 concentrations in men with prostate cancer with suppressed endogenous E2 production arising from androgen deprivation therapy (ADT) were determined. Furthermore, the short-term biological effects of E2 addback without increasing circulating testosterone (T) were determined. A rise was noted in the median serum E2 concentrations into the reference range reported for healthy men, but with substantial variability in men with castrate levels of E2 and T, daily transdermal E2 (0.9-1.8 mg). E2 treatment reduced hot flushes and bone resorption.