Fetal antigen 1 (FA1) is a circulating glycoprotein containing six epidermal growth factor (EGF)-like repeats. FA1's larger membrane-bound precursor is defined by the cDNAs referred to as either human delta-like (dlk) or human adrenal specific cDNA, pG2. In rodents FA1 has also been studied under the names of preadipocyte factor 1 (Pref-1), and zona glomerulosa-specific factor (ZOG). FA1 is abundantly expressed in fetal tissues, but in the mature cells of the, adult organism the tissue presence of the protein seems to be restricted to neuroendocrine tissues. The present study demonstrates FA1 localisation in endocrine tissues of the adult female rat in which the protein was found present in the medulla and the zona glomerulosa of the cortex of the adrenal glands, in the pars distalis of the adenohypophysis, and in the ovarian granulosa lutein cells. No staining was found in the pancreas, which is in contrast to what has been described in the human.