Cellular interactions in the rat testis are suggested by the presence of gap junctions between developing germ cells and Sertoli cells as well as tight junctions between adjacent Sertoli cells. Cadherins are cell surface proteins that mediate calcium-dependent intercellular adhesion. In these experiments the presence and developmental regulation of three cadherins have been examined: epithelial cadherin (E-Cad), neural cadherin (N-Cad), and placental cadherin (P-Cad). Northern blot analysis of testicular RNA indicates the presence of N-Cad [4.3 and 3.5 kilobases (kb)] and P-Cad (3.5 kb) transcripts. No E-Cad message was detected. To determine whether mRNA concentrations for P-Cad and N-Cad are regulated during postnatal rat testicular development, testes from rats ranging in age from 7-91 days were subjected to Northern blot analysis. Relative P-Cad mRNA levels were highest at 7 days of age and decreased to almost half of these levels by day 14. P-Cad mRNA levels subsequently decreased to low levels and remained constant thereafter. This contrasted with the developmental pattern observed for the 4.3-kb N-Cad transcript, which was low early in testicular development but increased to peak levels on day 42, coincident with the shedding of the first sperm. N-Cad mRNA concentrations decreased from 42 to 56 days and then remained constant until 91 days. While mouse P-Cad antibody did not cross-react with rat P-Cad, immunoblots of testicular membrane protein preparations identified the presence of immunoreactive N-Cad protein in the testis. The presence of N-Cad protein confirms that N-Cad mRNA is translated in this tissue. The developmental patterns of P-Cad and N-Cad mRNA suggest a role for P-Cad early in testicular development, while N-Cad appears to play a role in later stages of spermatogenesis.