SUMMARYA simple, easily prepared medium for countingClostridiumspores is described. With yeast extract starch bicarbonate (YESB) agar, counts of mildly heated (75°C. for 60 minutes) spores of 5Clostridiumstrains were consistently comparable to those secured in a modification of Yesair's pork infusion medium, with or without added bicarbonate. Omission of bicarbonate from YESB agar resulted consistently in a small but significant decrease in counts withCl. Botulinum62A. Addition of bicarbonate to the Yesair medium resulted in increased counts and earlier colony development withCl. botulinum62A.With spores of 6Clostridiumstrains heated at 100°C. for a period sufficient to insure at least 99.95% destruction, recovery counts in YESB were comparable to those in modified Yesair's medium, with no evidence of dormanc