A rapid method of volatile analysis and interpretation is taught enabling inferences on the surrounding environment as sophisticated as commonly achieved by dogs via olfaction. The method is based on rapid analysis of vapors released by persons or other organisms into a gas, correction of said analysis due to competing ambient volatiles, extraction of abundance patterns of certain preselected metabolites present in said vapor analysis, and classification of said persons or organisms by comparison of said abundance patterns with preestablished standard metabolite patterns. A preferred approach for rapid analysis involves an atmospheric pressure ionization, such as an electrospray cloud, followed by a mass spectrometer with an atmospheric pressure source. A preferred method for background correction is subtraction of the background signal from the sample signal when both are ionized at similar humidity levels. A preferred comparison pattern involves the abundance of fatty acids and other common metabolites. Preferred classification criteria include recognition of individuals, or species, or health state.