Sporeforming bacteria are present in practically all raw milk, but usually in small numbers if the milk is produced under modern sanitary conditions. There appears to be no relationship between total bacteria and spore counts, nor between total bacteria and the incidence of any given species of sporeforming organism. Bacillus species account for about 95% of the total sporeforming bacteria in milk, with Clostridium species comprising the remainder. In the United States, approximately 43% of the Bacillus organisms are B. licheniformis and 37% are B. cereus. Reports from some other countries indicate a predominance of B. cereus, or essentially a reversal in the prevalance of these two species. Spores of both these organisms survive low temperature pasteurization, some persisting through even the lower temperatures in the ultra-high range, and recent reports indicate that some sporeformers are psychrotrophic. B. cereus has been implicated in outbreaks of food-borne illness, but this is still controversial. Should B. cereus be proven capable of growing in the psychrotrophic range, and also responsible for food-borne illness, then the significance of spores in milk would take on added importance.