Pulmonary metastases from tumours of the testis are, of course, not uncommon, but they are usually multiple, resembling “golf balls” in appearance and are seldom very large or solitary. The following two cases are worthy of record because the X-ray appearances of the lungs simulated hydatid cysts, and, more especially in the first case, created a diagnostic problem. J.P.M., aged 30, was admitted into Mount Vernon Hospital under my care on 6.2.45 complaining of abdominal swelling and dyspnœa on exertion. There was no cough, expectoration or haemoptysis. He had a left orchidectomy performed at St. Thomas's on 1.6.43 and histological examination showed that the growth was a teratoma testis. The operation was not followed by deep X-ray therapy and five months after the operation the patient joined the Royal Marines. He kept well for a time but later noticed a swelling in the abdomen which, however, caused no symptoms. He subsequently had a fainting attack, and, reporting sick, was medically examined and an X-r...