Based on the concept of sequence conservation around the active sites of serine proteinases, polymerase chain reaction applied to mRNA amplification allowed us to obtain a 260-bp probe which was used to screen a mouse pituitary cDNA library. The primers used derived from the cDNA sequence of active sites Ser* and Asn* of human furin. Two cDNA sequences were obtained from a number of positive clones. These code for two similar but distinct structures (mPCl and mPC2), each being homologous to yeast Kex2 and human furin. In situ hybridization (mPCl) and Northern blots (mPCl = 3.0 kb and mPC2 = 2.8 and 4.8 kb) demonstrated tissue and cellular specificity of expression, only within endocrine and neuroendocrine cells. These data suggest that mPCl and mPC2 represent prime candidates for tissue-specific pro-hormone converting proteinases.