Sixteen patients with severe coronary artery disease and unstable angina, refractory to standard therapy with nitrates, beta-blockers or calcium antagonists, were given intravenous nitroglycerine (500 micrograms/ml) in an open trial. The infusion was started at 0 . 17 ml/min. The final infusion rate ranged from 0 . 17 ml/min to 2 . 04 ml/min, depending on the symptomatic and haemodynamic response of the individual patient. At the slow infusion rates, the actual dose was probably only 15% of the delivered dose because of the absorption of nitroglycerine to PVC tubing. There was significant pain relief in all patients. In six patients, pain relief was complete; in ten patients, occasional episodes occurred during the nitroglycerine infusion but they were less frequent and less severe and few were associated with ST segment changes. Systolic blood pressure fell by a mean of 100 mmHg at the commencement of therapy but there was no significant change in heart rate. Apart from mild headaches, no other adverse effects were observed. The mean treatment time was 3 . 2 days (range 1-8 days). Eight patients were discharged on oral and/or cutaneous nitrate therapy and eight patients had coronary artery surgery.