A setup for measuring the lifetime of free electrons in a neutral buffer gas that contains an electronegative impurity is described. This setup is intended for prompt diagnostics of carcinogenicity of chemical compounds and consists of an ionization chamber with laser photoionization of the cathode, a gas system, and a system for collection and processing of experimental data based on an HBJI45 amplitude-to-digital converter. The techniques for preparing the tested gaseous mixtures and processing the experimental results are described. The results of measurements of the lifetimes and calculated free-electron capture constants for a CO2 + O2 calibrating mixture and mixtures of CO2 with organic molecules are presented. The setup allows measurements of the lifetimes of free electrons in mixtures in the range 0.5–70 μs at measurement errors of 0.2–6%, respectively, and study of two or three potentially carcinogenic substances a week.