The question is addressed whether cisplatin-based chemotherapy for germ cell cancer has the same efficacy in intratesticular and in extragonadal sites. For this purpose, 7 patients with germ cell cancer, aged 16-35 years were analysed. Four of the patients had palpable testicular tumors, 3 had occult testicular tumors. All presented with advanced disease and therefore received chemotherapy as the first step of treatment. Orchiectomy was done in the later course. A significant clinical response to chemotherapy was observed at the intratesticular tumor site as well as at extragonadal sites in all patients. Orchiectomy specimens contained viable cancerous cells in 2 patients after two courses of chemotherapy while in 5 patients no invasive germ cell cancer was found. Severe depression of germ cells was observed in all specimens. Testicular intraepithelial neoplasia (TIN; carcinoma in situ) persisted in 4 patients, 1 of whom also had viable cancerous cells in the specimen. Cisplatin-based chemotherapy is also active in intratesticular tumors but there seems to be a slightly different response of metastatic germ cell cancer and intratesticular tumor. Tumor heterogeneity appears to be the most important reason for this different response. The lower response of TIN to chemotherapy as compared to invasive testicular cancer is probably due to a genetically determined lower sensitivity. The blood-testis barrier might contribute a minor part to this phenomenon by modulating the intratubular concentrations of cytostatic compounds. The efficacy of cisplatin-based chemotherapy on invasive intratesticular tumors is not compromised by the blood-testis barrier.(ABSTRACT TRUNCATED AT 250 WORDS)