OBJECTIVE The frequency of gonadoblastoma is high in patients with Turner's syndrome bearing cells with Y or partial Y-chromosome. About 60% of patients with Turner's syndrome have a 45,X karyotype. In 30% of them a Y-sequence is disclosed by DNA analysis. To identify patients at risk of developing gonadoblastoma, a PCR based assay with SRY, ZFY and DYZ3 specific primers was carried out to detect different Y-sequences in the DNA of peripheral lymphocytes from patients with Turner's syndrome. METHODS Peripheral blood karyotypes from 36 patients with Turner's syndrome were studied. Patients with proven Y-chromosomal material were excluded. Genomic DNA was extracted from peripheral blood. SRY and ZFY genes and DYZ3 repetion of Y-chromosome were amplified by PCR. Patients with clinical signs of hyperandrogenism or with positive Y-sequences by PCR underwent gonadectomy. The gonadal tissues were examined for Y-sequences using PCR, morphology and immunohistochemical study. METHODS Turner's syndrome and signs of hyperandrogenism were evaluated both clinically and through laboratory tests. Haematoxylin and eosin staining was employed in gonadal morphology studies. The presence of testosterone was detected by immunohistochemistry using a monoclonal antibody. RESULTS Two patients who had Y-positive blood samples and three hyperandrogenic (2 hirsutes, 1 virilized) Y-negatives underwent gonadectomy. PCR was carried out on their gonadal tissue. The tissue from the two patients without hyperandrogenism was Y-positive. The gonadal tissue from the three hyperandrogenics was Y-negative. Gonadal morphology disclosed hilus cell hyperplasia in the 3 hyperandrogenic Y-negatives and in one Y-positive patient; stromal luteoma and hyperthecosis in the virilized patient, cystadenofibroma in one hirsute patient and gonadoblastoma in one Y-positive. Testosterone was detected immunohistochemically in the hilus cell hyperplasia, stromal luteoma and hyperthecosis found in the hyperandrogenic patients. CONCLUSIONS The molecular study was sensitive and useful in the evaluation of patients at risk of developing gonadoblastoma. Other nontumour, gonadotrophin-dependent and Y-independent mechanisms which deserve the same medical approach may be involved in the genesis of hyperandrogenic signs in Turner's syndrome.