Acetate selection and biochemical tests were used to characterize the gram positive, spore-forming bacteria associated with samples of straw and sawdust used as bedding in outdoor calf hutches. Bedding samples were collected from 25 calf-occupied hutches during 6-wk periods. More than 7,100 isolates representingBacillus thuringiensis(4,616),Bacillus sphaericus(1,390), andBacillus megaterium(1,182) were recovered. Fourteen biochemical types ofB. thuringiensiswere identified; these includedgalleriae, kurstaki, thuringiensis, israelensis, sotto, darmstadiensis, tenebrionis/morrisoni, dendrolimus, andindiana. Of these,tenebrionis/morrisoniandisraelensiswere associated most often with tulip poplar and maple sawdusts, respectively. Tulip poplar sawdust supported more diverseB. thuringiensisbiochemical types than other types of sawdust or straw.B. thuringiensiswere prevalent in calf-hutch bedding throughout 6-wk periods.