The 18G Biopty biopsy has been evaluated as a tool to detect carcinoma in situ in the remaining testes of patients with extragonadal germ cell tumours or unilateral germ cell tumours. In all, 68 biopsies were performed in 57 selected patients. Five carcinomas in situ and 1 infiltrative seminoma were detected. The biopsies were performed under local anaesthesia. Pain and/or haematomas occurred after 9 of the 68 biopsies but none of the haematomas required invasive measures. This method of performing biopsies from clinically tumour-free testes seems promising but longer follow-up is required to evaluate the sensitivity of the method compared with open surgical biopsy.