A number of cysteine-rich proteins have recently been isolated by homology screening, differential library screens, and association with other proteins. In this report, we describe the isolation of the rat cysteine-rich protein from a rat brain library during a search for clones with homology to the delta-opioid receptor. One of the cDNAs isolated hybridized to a 1.8 kb mRNA abundantly expressed throughout the rat brain as well as in rat liver. In situ hybridization reveals a wide distribution in rat brain; in particular, abundant hybridization was detected in the hippocampus, cerebellum, habenula, reticular thalamic nucleus and interposed nucleus. Nucleotide sequence analysis of a 1403 bp cDNA clone indicated 77% identity with the cDNA for human cysteine-rich protein (hCRP), that translates into a 99% identity at the amino acid level. The predicted amino acid sequence suggests four zinc fingers, two of the C4 class and two of the C2HC class. This structural motif is characteristic of members of the LIM domain protein family. The mRNA is serum-inducible in Balb/c 3T3 cells. Additional study suggests that its expression is not induced by either NGF treatment of PC12h pheochromocytoma cells, or inflammation-induced injury in the spinal cord at up to 60 min after injury. It does appear to be developmentally expressed in rat brain, consistent with a potential role in neuronal development. The rat CRP clone will be useful for studying the function of CRPs in rodent models.