Previous studies have shown that NGFI-B mRNA is highly expressed in the adult striatum. We analyzed the anatomical distribution of NGFI-B mRNA within this brain region as well as the degree of co-existence of NGFI-B with different striatal markers in the adult brain. NGFI-B mRNA levels were found to be significantly higher within the dorsomedial portion of the striatum as compared to the ventrolateral striatum. This distribution pattern was maintained throughout the rostro-caudal axis of the striatum. Double in situ-hybridization studies showed that striatal NGFI-B mRNA co-localized with a subset of preproenkephalin and prodynorphin positive spiny neurons within the dorsomedial striatum; 22-28% of all opiate-peptide positive cells co-expressed NGFI-B mRNA. NGFI-B did not co-localize with striatal aspiny interneurons expressing choline acetyl transferase mRNA or those containing the calcium-binding protein parvalbumin. The pattern of NGFI-B mRNA expression within different striatal spiny projecting neurons suggest that this transcription factor may have a direct effect on the function of different striatal efferent pathways.