Bacillus subtilis spores were immobilized in activated charcoal and tapioca and filled with acacia gum. These formulations were tested for spore stability during storage at temperatures ranging from 40 degrees C to 90 degrees C and for bacterial release. Thermodynamic analysis showed that immobilization of spores in acacia gum significantly increased their viability compared with unprotected spores. The viability was further increased when suspensions of spores in acacia gum were added to granules of charcoal and tapioca. The number of the spores released after storage was also increased when spores were treated with acacia gum prior to immobilization in tapioca and charcoal. Formulations of Bacillus spores with acacia gum and porous carriers (charcoal and tapioca) prolong the anticipated shelf-life of spores even under ambient temperature and provide slow and steady bacterial release consistent with their high viability.