T HE Medical Research Council's investigation into pityriasis rosea in 1959 has already been published (Proc. roy. Soc. Med., 55, 556). This second investigation, based on a very simple questionnaire, has produced some additional information, but has not altogether solved the question put, namely "What is the cause of this disease?" Much interest was shown. In 1964, 180 observers notified 531 c...