The bacteriocidal efficacy of Purogene, a stabilized aqueous solution of chlorine dioxide (ClO2) was examined using bacteria of concern to public health. The organisms tested were: Escherichia coli, Pseudomonas aeruginosa, Yersinia enterocolitica, Klebsiella pneumoniae, Streptococcus pyogenes Group A, Salmonella typhimurium and Bacillus subtilis. The test organisms responded differently to inactivation by Purogene. At least a 4 log reduction in bacterial counts was noted when Purogene was applied at a concentration of 0.75 mg/l. Since Purogene is a stabilized complex, it was necessary to provide a chemical environment suitable for the release of ClO2 in this solution. This was done by varying the pH of Purogene from 3.5 to 8.6 (pH of Purogene is 8.6) while keeping the pH of the experimental medium constant (pH 7.0). The results showed that Purogene was most efficacious at the lowest pH tested (pH 3.5). This indicates that as chlorine dioxide solutions were reduced to chlorite (which predominates at pH 8.6), their bacteriocidal efficacy was reduced, suggesting free chlorine dioxide as the active disinfecting species.