A fragment of human genomic DNA containing the entire pro-opiomelanocortin (POMC) gene was introduced by transfection into the rat glial cell line C6. Blot analysis using poly(A)-rich RNA from the transformed C6 cells showed several hybridization bands. One band was similar in size (1·2 kb) to the POMC mRNA of human pituitary, while two were larger (2·6 and 2·2 kb) and the fourth smaller (800 bp). S1 nuclease mapping revealed that the POMC transcripts in transformed C6 cells were similar to those in non-pituitary tissues. Immunoreactive ACTH (ir-ACTH) was measurable in both the culture medium and cells. Gel chromatography showed that ir-ACTH in the medium eluted at a position identical to that of so-called big ACTH (approximately 40 kDa) which is found in the plasma of patients with ectopic ACTH syndrome. The human POMC gene could thus be expressed in the non-pituitary rat glial cell line C6, although the transcripts and translation products in C6 cells differ from those in the human pituitary. These results suggest that the transformed C6 cell may be a useful tool for studying the regulation of human POMC gene expression in non-pituitary cells.