SummaryFour cases are presented in whom transthoracic aspiration biopsy with the rotex needle provided a specific diagnosis, which, on thoracotomy was proved•ncomplete or wrong. Two cases of abscess were in fact excavated squamous cell carcinomas, one case of tuberculosis was in fact accompanied by a scar-adeno-carcinoma, and a fourth case of supposed small cell carcinoma was found to be a muco-epidermoid carcinoma. In all cases, the final diagnosis after thoracotomy led to a change in therapy.