Ahh....I see. Your answer to the puzzle is that the frontal hair follicles of the juvenile, pre-balding stumptailed macaques DID INDEED have an intrinsic sensitivity to androgens (in the sense that they would suppress the growth of keratinocytes that were co-cultured with them), it's just that the level of androgen receptors in the hair follicles of those youthful monkeys was so low that the suppressive effect wasn't obvious to the researchers. Doctor, the only problem I have with that is that there was no mention of any such hypothesis from Uno and his colleagues in that study. They seem to be as puzzled by that as the rest of us (other than you and, of course, Stephen Foote! :wink: ) who have discussed this aspect of the experiment from time to time. Doesn't it seem likely that someone as experienced and famous in the field of hairloss research as Hideo Uno would have suggested such an explanation, if he felt it was reasonable? What I get from the text of that study is that the levels of androgen (testosterone) that they used should have been sufficient to produce _some_ kind of a noticeable suppressive effect, even if there were lower levels of androgen receptors in the young monkeys. BTW, how do you explain Sawaya's claim of finding an "intense upregulation" in the numbers of androgen receptors in the hair follicles of finasteride users? That would appear to contradict what you said above (greater androgenic stimulation upregulates androgen receptors). Furthermore, a separate study ("RNA-Levels of 5a-Reductase and Androgen Receptor in Human Skin, Hair Follicles and Follicle-Derived Cells", Eicheler et al, from the book "Hair Research for the Next Millenium", 1996) found that adding testosterone to cultures of human scalp hair follicle papilla cells DOWN-regulated androgen receptor RNA, which would seem to support Sawaya's findings and contradict the theory that androgens UP-regulate androgen receptors (at least specifically in human scalp hair follicles). Do you have any thoughts on all that? And Stephen Foote, why have YOU remained silent on this? What do you think of docj's answer to the pre-pubertal macaque puzzle?