The involution of the prostate that occurs after castration is thought to be an active process, requiring protein synthesis. A number of "castration-induced" proteins which might be involved in this process have been identified. We recently described a group of "testosterone-repressed" mRNA sequences in the prostate which could code for these proteins. Because of their potential importance in the autophagic response we have cloned these sequences, and we report here the characterization of the most abundant of these sequences (TRPM-2), and the kinetics of the induction of this gene in the prostate after castration. TRPM-2 is induced to a maximum level of approximately 1440 ppm of total RNA six days after castration, by which time the androgen dependent, prostate steroid binding protein (PSBP) mRNA sequences have diminished to undetectable levels. The translation product of TRPM-2 is a protein of approximately 46,000 daltons, with a pI of 5.9-6.3. Since this gene is expressed in other involuting tissues, it may play an important role in the process of tissue regression.