Cryopreservation is shown to be a suitable technique for storing Streptococcus mutans prior to analysis of chemicals for putative antibacterial properties by microcalorimetry. Excellent recovery of cryopreserved cells was obtained and their response in the microcalorimeter was highly reproducible. Linear responses were obtained when the concentration of fluoride was varied in assays. Similar results were obtained with natural products claimed to have antimicrobial properties. It is proposed that microcalorimetry with cryopreserved cells could be used as a method for rapidly assessing the potential of individual or mixtures of components for commercial preparations designed to control oral microflora.