A rapid method is described for the determination of biochemical variants of mice by Titan III cellulose acetate electrophoresis. Variants examined were hemoglobin beta-chain, serum esterase-1, malic enzyme (supernatant form), and isocitrate dehydrogenase (supernatant form). The present procedure can be recommended as a simplified method to analyze biochemical variants for checking of marker genes in inbred strains of mice.