A computer program, SpectraSort, has been written to facilitate the analysis of ambient aerosol data acquired in our laboratory using aerosol time-of-flight mass spectrometry (ATOFMS). ATOFMS is a unique aerosol analysis technique developed to obtain the size and chemical composition of individual aerosol particles. Conventional aerosol analysis methods can only provide the average chemical composition of many particles for a given size range, or the size of individual particles, but not their chemical composition. Knowledge of both the size and composition of individual aerosol particles ultimately will help evaluate particle toxicity and reactivity, as well as assist in the identification of particle emission sources. These three pieces of information are vital in any rigorous attempt to regulate particulate pollution in the atmosphere. At present, in ATOFMS data analysis, each individual particle mass spectrum must be calibrated manually, and any compositional information tabulated for subsequent correlation with the size of the corresponding particle. SpectraSort greatly facilitates the processing of particle size and composition information by maximizing the efficiency of manual classification; but, a fully automated solution is necessary if ATOFMS is to evolve into a routine real-time aerosol analysis tool.