During the past 28 months, 60 patients with suspected acute myocardial infarction (AMI) were admitted to a prehospital satellite industrial coronary care unit (SICCU). During patient stabilization, clinical data, blood studies and continuous electrocardiographic tape recordings were obtained. Thirty-three of the 60 patients had AMI, and the median SICCU arrival time was 45 minutes. Seventy-seven percent of the patients had one or more ventricular premature beats (VPBs) on the 78 ± 11 minute ECG tape recording, and 36% of the AMI patients developed major ventricular arrhythmias within 24 hours of the initial observation. Closely coupled VPBs and elevated cortisol levels were reliable prehospital precursors of serious ventricular arrhythmias. Early prehospital arrival, atrial bradycardia, frequent VPBs, hypertension, elevations of growth hormone or nonesterified fatty acid (NEFA), and decreased insulin levels lacked significance as indicators of subsequent ventricular arrhythmias.