MemDers of the Bacillus maceram-polymyxa group of bacteria have not been included among the major groups of canned food spoilage organisms even though Cameron, Esty, and Williams ( 7 ) proved a related species, B. betmigrificans: to cause "black beets" and other mesophilic members of the genus are well known for their ability to spoil a variety of such foods. .] Nevertheless, since 1943 several outbreaks of canned food spoilage have been observed in which it was possible to incriminate either B. macerans o r B. polymyxa or a mixture of these 2 species as the cause of the spoilage. Gas formation, principally carbon dioxide but with some hydrogen, was the chief characteristic of all outbreaks. Sometimes tissue disintegration or polysaccharide (gum) formation was associated with the spoilage. Both tin and glass containers were involved in several outbreaks of spoilage observed in commercially canned fruits and vegetables and in home-canned fruits.The first commercial outbreak called to the attention of the authors from which the facultative aerobic, gas-forming bacilli were isolated occurred in ppasd packed in glass with a vacuum closure. Cooling water, heavily contaminated with the spores of the B. macerans-polymyxa group of bacteria, was "breathed" into the jars through a defective sealing surface (finish) which finally was closed b y the rubber gasket before cooling was completed. I n the second commercial outbreak of spoilage the same types of bacteria were recovered from fruits (cling peaches and a diced fruit mixture of cling peaches and pears) packed in tin cans. The exact cause of this second outbreak was not determined. The suspected bacteria were found in large numbers in the plant water supply and in the syrups used for packing the fruits as well as in the cooling water. Furthermore, the p H values of some of the cut-out syrups from sound cans were as high as 4.4, indicating excessive neutralization of the fruit which had been iye peeled. Consequently, opinion was divided .as to whether cooling water contamination resulting from "breathing " or borderline processing was "Present address : Curtis and Tompkins, Ltd., San Francisco, California. 'This species is considered t o be synonymous with Bacillus macerans by Smith, Gordon, and Clark (3'2).dThe peas represented an out-of-state outbreak of spoilage not observed at first hand. W. E. Parks graciously supplied samples of spoiled peas as well as cultures which had been isolated at the source.