NOR-1 is a novel member of the NGFI-B/RNR-1 subfamily within the nuclear receptor superfamily, and has been implicated in signal transduction mediated by various second messengers. To investigate the physiological role of NOR-1, we examined its gene expression in various adult rat tissues and developing rat brain by the quantitative reverse transcription-polymerase chain reaction using in vitro synthesized RNA as an internal standard. The NOR-1 gene was expressed in all tissues examined, but predominantly in the cerebral cortex and pituitary glands. Thymus, adrenal glands, spleen, epididymis, submandibular glands and deferent ducts showed moderate expression. In the brain, NOR-1 gene expression was developmentally regulated, with the peak levels on gestational day 18. These findings suggest a ubiquitous role of NOR-1 in signal transduction in diverse tissues. These findings also suggest that the nervous, endocrine and immune systems may be highly exposed to NOR-1-inducing stimuli under normal conditions in adult rats. Developing rat brain cells may most frequently receive the relevant signal on day 18 of gestation.