Virilizing adrenal tumours, adenomas and adenocarcinomas are rare and their clinical manifestations vary depending on age at onset. The paper reports the results obtained in 4 patients with adenoma and 3 with adenocarcinoma, as well as 11 cases of classic congenital adrenogenital syndrome by way of comparison. The hormonal status of adenomas is usually characterised by a predominant increase in plasma androstenedione (> 600, ng/dl) and testosterone (> 200 ng/dl), whereas carcinomas present a predominant hypersecretion of dehydroepiandrosterone (> 1200 ng/dl) and its sulphate (> 700 micrograms/dl). Plasma estrogen levels may also be enhanced due to active peripheral androgen conversion or direct secretion. 17alpha-hydroxyprogesterone, which is high in congenital adrenal hyperplasia, is normal or slightly enhanced, as is cortisol. Differential diagnosis must be made with androgen secreting tumours of the ovaries and, in males, with the various forms of precocious puberty, including endocrine tumours of the testicle, as well as congenital adrenogenital syndrome. A tumour with a diameter > 7 cm when examined using CT or NMR may be suspected as carcinoma, but malignancy cannot be excluded even in smaller tumours. Virilizing adrenal tumours do not usually respond to dexamethasone suppression test or ACTH stimulus since they do not express ACTH receptors or present post receptor anomalies. Steroidogenesis may be cAMP/protein-kinase independent and can be activated through alternative pathways. The presence of a stimulating G-protein has been detected in carcinomas which serves to activate adenylate cyclase on a permanent basis. b6 cytochrome is super-expressed and may be responsible for androgen over-secretion by activating 17,20-desmolase.(ABSTRACT TRUNCATED AT 250 WORDS)