An analytical method for quantitation of the RNA transcripts of murine bcl-2 gene was developed. The PCR products from bcl-2 alpha and bcl-2 beta mRNA were fluorometrically analyzed and their specific contents were calculated by the internal standard method. Both bcl-2 mRNAs in adult mice were transcribed at the highest level in the thymus and at a comparable level in the spleen. Aside from the immune system, the brain gave the most abundant levels of the bcl-2 mRNAs. The ratios of bcl-2 beta mRNA to bcl-2 alpha mRNA in the thymus and spleen were significantly higher than those in other tissues. During development of the brain, the bcl-2 alpha and bcl-2 beta mRNA levels were highest on embryonic day 15, and about two and three times higher than those of adult, respectively. The results suggest that the bcl-2 gene functions to regulate development and survival of neurons in the central nervous system.