Book excerpt: It is now thirty years since William Montagna and Richard Ellis edited 'The Biology of Hair Growth". In his introduction, Stephen Rothman, of the University of Chicago, USA and one of the driving forces behind research on skin at the time, wrote: 'The pilary system is a perfect micr9cosmic structure. In this microcos mos we find birth, development, ageing and death, activity and rest, color for mation and decolorification, greasiness and dryness, infection and sterilization, hypertrophy and atrophy, Qenign tumours and malignant ones." He foresaw the human pilary system as a model for the study of a multitude of human diseases including ageing and cancer. It was not, how ever, until the seventies that the development of micro-biochemical tech niques indeed allowed the use of the human hair follicle as a convenient biopsy tissue for Biomedical Research in general. Measurement of enzyme activities, and important co-factors, and culturing of cells from single follicles all became possible. In the eighties dermal papilla cells were grown in cul ture and this opened the way to study hair differentiation in vitro. Studying hair differentiation is, in fact, studying growth regulation and it is this aspect that by far transcends the importance of studying hair growth itself. Let us not forget that metastatic prostate cancer is treated with the same drug -cyproterone acetate -that is used for the treatment of alopecia and hirsutism in women.