In response to a questionnaire regarding use of invasive hemodynamic monitoring techniques in the United Kingdom, 211 replies were received from 276 hospitals (76.4 percent). Over one fifth of Intensive Care or combined Intensive/Coronary Care Units did not use pulmonary artery catheters (PAC); of those that did, two thirds used no more than two/month, and only two units used more than ten/month. Nearly a quarter did not possess a cardiac output computer. Only 18 complications occurring in the preceding year were reported, which suggests underrecognition. Clinical indications and lack of expertise were the main reasons proferred for limited use; however, cost (which was generally underestimated) and clinical value also were mentioned. The majority of CCUs did not use PACs, and only 10 percent used more than two/month. Only 10 percent of hospitals have used them perioperatively and most cardiothoracic units used no more than two PACs/month. In view of the large difference in numbers used between the United Kingdom and the United States, a large-scale study is warranted to determine the actual value of PACs in reducing mortality and morbidity.