Struck by delays in the diagnosis of carcinomas of the prostate and testis, the authors have developed a method for cytological study by puncture of those organs. During a 7 year period, they saw 100 carcinomas of the prostate, 94% of which had already spread beyond the prostate with bone metastases in 48%. During the same period, 18 carcinomas of the testis were seen, with several erroneous differential diagnoses which led to a delay in diagnosis (mean: 12 weeks). The authors use a Franzen-type aspiration needle which makes possible puncture and aspiration of the tumour zone without hospitalisation of the patient. Cytological diagnosis implies the need for considerable experience, bearing in mind that in particular certain excessively deep punctures of the prostate may yield cells from the seminal vesicles which lead to an incorrect diagnosis of carcinoma of the prostate. Such aspiration cytology may be used to differentiate between benign and malignant tumours, as well as providing a more accurate diagnosis in terms of the type of tumour and the degree of differentiation.