The recent literature on acne, particularly the useful contribution by Cohen (1956) and the masterly exposition by MacKenna (1957), makes an introduction to the subject of acne and hair growth superfluous. However, as these authors make reference to some work of mine, which is not readily available in the medical literature, a publication of the essential facts on which my conclusions are based seems necessary. Observations The first step in elucidating the relationship between acne and hair growth was to follow up previously made observations on the subject. Following Milton's observations (1872) that hairs are not seen issuing from follicles blocked by comedones, I confirmed this by visual examination of more than 200 patients, especially patients with acne affecting the back. Here the hair pattern in many cases is sufficiently regular and coarse to make obvious to the naked eye the fact that a comedo has