The Cysteine-RIch Secretory Proteins (CRISPs) are abundantly produced in the male reproductive tract of mammals and within the venom of reptiles and have been shown to regulate ion channel activity. CRISPs, along with the Antigen-5 proteins and the Pathogenesis related-1 (Pr-1) proteins, form the CAP superfamily of proteins. Analyses of EST expression databases are increasingly suggesting that mammalian CRISPs are expressed more widely than in the reproductive tract. We, therefore, conducted a reverse transcription PCR expression profile and immunohistochemical analyses of 16 mouse tissues to define the sites of production of each of the four murine CRISPs. These data showed that each of the CRISPs have distinct and sometimes overlapping expression profiles, typically associated with the male and female reproductive tract, the secretory epithelia of exocrine glands, and immune tissues including the spleen and thymus. These investigations raise the potential for a role for CRISPs in general mammalian physiology.