Persistent carcinoma in situ of the testis after chemotherapy for advanced testicular germ cell tumours. The chemosensitivity of testicular carcinoma in situ (CIS) was analysed in 25 testes excised 10 weeks to 4.5 years following platinum-based chemotherapy. CIS was present in 8 of the 23 evaluable cases (35%), in 5 of which the lesion coexisted with invasive germ cell tumour. It is concluded that CIS may persist or recur after chemotherapy. This has implications for occult presentation of metastatic germ cell tumours and also for the management of the contralateral testis in patients with testicular germ cell tumours. 