We analyzed the expression profiles of several steroidogenic enzymes in normal adrenals, aldosterone-producing adenomas (APA), cortisol-producing adenomas combined with Cushing's syndrome (CPA) or with subclinical Cushing's syndrome (SCPA), and nonfunctioning adrenal adenomas (NFA) to clarify the nature and characteristics of steroidogenesis in APA. Clinical data were collected for all subjects. In resected adrenal glands (normal adrenals, APA, CPA, SCPA, and NFA), the mRNA expression levels of the CYP17, HSD3B2, CYP11B1, and CYP11B2 genes were studied using real-time quantitative PCR and immunohistochemistry. The CYP11B2 mRNA level in APA was significantly higher than that in other groups. The CYP17/HSD3B2 ratio for mRNA in APA was significantly lower than those in the other groups. Low ratio of CYP17/HSD3B2 with high expression of CYP11B2 seems to explain steroidogenic characteristics of APA.