We have adopted a polymerase chain reaction approach to identify and clone a cDNA that contains the complete coding sequence of a novel fatty acid binding protein (FABP) from a rat brain λgt10 library. Sequencing of the brain FABP (B-FABP) cDNA revealed an open reading frame coding for a protein with 132 amino acids and a predicted size of ∼15,000 Da. This putative protein shares extensive sequence homology with other members of the FABP family. Northern blot analysis using the B-FABP cDNA as a probe established the presence of an abundant mRNA ∼0.8 kb long in rat brain and in the MOCH-1 oligodendrocyte cell line. This transcript was also present in rat liver but not in other tissues examined. A developmental profile of this mRNA in rat brain demonstrated detectable expression in 15-day-old embryos with levels peaking in 1-day postnatal neonates and declining thereafter, reaching a low steady-state level at 3 weeks of age. In situ hybridization histochemistry revealed B-FABP mRNA in various brain regions, with the highest levels in fiber tracts. The B-FABP message was also detected at a lower level in several gray matter regions. The cloning approach used in this study would likely be useful in the identification and isolation of FABP-encoding genes from other tissues and species.