To the Editor.— Regarding "Pityriasis Rubra Pilaris: Prolonged Treatment With Methotrexate" by Knowles and Chernosky in theArchives( 102 :603. 1970), and in view of some work I have done with vitamin A and reported cases of successful therapy with vitamin A, I would like to make these comments. Reported success of treatment in some cases of pityriasis rubra pilaris (PRP) with vitamin A suggests that it can help, possibly acting as an antimetabolite. Failures with vitamin A therapy suggest a metabolic disorder of vitamin A metabolism or improper dosage. In my communication, "Treatment of Ichthyosis,"1 I reported excellent results in ichthyosis hystrix by using two adjuvants to increase vitamin A absorption and utilization, neostigmine (Prostigmin) to increase bowel activity, and bile salts to promote absorption. This has not been noted since attention was paid only to the salt therapy that I described. In Knowles and Chernosky's