Serum DHT, testosterone, the sum of 2 androgens, and serum estradiol levels measured with RIAs (left panel), and serum androgen bioactivity (ABA) measured with the bioassay (right panel) in 14 elderly men before and after 6 months of daily transdermal DHT treatment (7.5-10 g of 2.5% DHT gel applied to upper arms/shoulders or to the abdomen daily) as described in "Materials and Methods." Mean values with SEM are shown. ^***P < .0001. ^**P < .01.