Finkelstein JS, Lee H, Burnett-Bowie SAM, et al. - In the present study, the researchers sought to describe the dose-response links between gonadal steroid concentrations and measures regulated by gonadal steroids in older men. One hundred seventy-seven men between 60 and 80 years of age were randomly allocated to receive goserelin acetate plus either 0 (placebo),1.25, 2.5, 5, or 10 grams of a 1% testosterone gel daily for 16 weeks, or placebos for both medications (controls). Clear associations were established between the dosage of testosterone (or the resulting levels of testosterone) and a number of outcome measures. Data reported that changes in serum C-telopeptide exceeded changes in the controls in men whose testosterone levels were 0-99, 100-199, 200-299 ng/dL, or 300-499 ng/dL while increases in total body fat, subcutaneous fat, and thigh fat exceeded controls when testosterone levels were 0-99 or 100-199 ng/dL. Changes in bone resorption, body fat, and sexual function measurements begin at a variety of testosterone concentrations with several outcome measures remaining stable until the levels of testosterone are well below the specified normal range. With this variation in mind, novel approaches are needed to establish the normal testosterone range.