The rodent prolactin (PRL)/growth hormone (GH) gene family currently consists of at least 14 distinct genes that are expressed mainly in pituitary, uterus, and/or placenta. We report here the identification of novel four members from rat with significant homology to PRL. The encoding proteins are not homologs of other known members of this hormone family. The four new cDNAs were assigned to PRL family based on sequence homology and were referred to as PRL-like protein-I (PLP-I), PLP-J, PLP-K, and PLP-L, following the current naming order of rodent PLP family, where PLP-H is the most recent gene. They encode amino acids with 211–228 amino acids, and 34–38% identity with PRL. All have one or two N-linked glycosylation sites. Among the examined rat tissues by Northern blot analysis, only PLP-I was expressed in testis. Our results indicate that the rodent PRL/GH gene family is large with at least 18 distinct genes.