We previously reported that ACTH receptor (ACTH-R) mRNA is expressed in cortisol-secreting adrenal tumors, with significant differences between adenomas and carcinomas. In order to complete the study we have now evaluated 11 aldosteronomas (APA), 14 non-hypersecreting adenomas, 2 androgen-secreting adenomas and 8 normal adrenal glands. The level of ACTH-R mRNA was evaluated by competitive RT-PCR using a non-homologous competitor. ACTH-R gene was expressed in all tissues. All APA showed highest ACTH-R mRNA levels. Despite signs of individual heterogeneity, the level of ACTH-R transcripts was reduced in carcinomas. Furthermore, no significant differences were observed among cortisol-secreting adenomas, non hypersecreting adenomas and controls. The results show that ACTH-R mRNA is expressed in all adrenocortical tumors. The overexpression of ACTH-R in APA supports the role of ACTH on aldosterone secretion in these tumors, as also suggested by the presence of a diurnal rhythm, the lack of response to Angiotensin II, upright posture and captopril administration. The low abundance of ACTH-R in carcinomas might be a useful molecular marker of malignancy even if some overlap between carcinomas and adenomas does exist.