Investigations described in this paper are related entirely to the recovery of viable spores of PA-3679 and Clostridium botulinum type B. Spores of the respective test organisms were subjected to thermal treatment and gamma radiation independently. Questionnaires were distributed in January, 1957, to 26 individuals at various laboratories whose personnel have been interested in spore recovery after exposure to either heat and/or radiation. Information relative to recovery media used in counting anaerobes was requested. The cooperation of the recipients was appreciated as it permitted the study of a rather broad spectrum of media.A widespread interest in counting anaerobic spores, particularly thermally treated spores, has been manifested since the early 1930's. At processing conferences held in conjunction with the annual convention of the National Canners Association, the subject has been regularly discussed. Periodic attempts have been made to procure uniform procedures for thermal death time studies, and spore counting has been one of the several facets.In a restricted National Canners Association Report (Z), data were presented based on the cooperative work of 7 laboratories. The type of media employed was only one of several variables investigated. The Institute of Food Technologists has for some years been interested in this phase along with other problems related to thermal death time work. I n 1952 the Western Utilization Research Branch, USDA, conducted a survey on spore counting media with Clostridiztin botuliizziiiz and the results were distributed in private communications.Frank and Campbell (1) reported that the recovery media employed in a study with PA-3679 had an effect on the thermal resistance values. Six media with modifications were studied.Replies to our questionnaire listed 20 different media. It was indicated that they are used under varying conditions, such as spore counts on processed and non-processed foods, as well as thermal death time work. Several were used for Most Probable Number determinations, others for colony counting, and others merely for the development of growth as indicated by gas formation with odor.