A study of the potential hazard to ambulance personnel posed by siren noise was conducted. Sound pressure levels were measured during siren testing inside the driver and patient compartments and at distances of 10 and 100 feet from a conventional cab chassis ambulance with modular body. The siren speakers were attached to the roof of the driver's cab or to the grill or front bumper. For each siren location, testing was conducted with the cab windows open and closed. The siren was operated in three modes for each test: wail, yelp, and European or hi/lo for approximately 15 seconds. Average noise levels did not depend on the mode of siren operation. Noise inside the ambulance was most intense when the speakers were located on the roof and the windows were open. Under these conditions, the driver experienced 109 decibels-A (dBA) and the patient 91dBA. The lowest noise levels inside the ambulance, 76 to 80dBA, occurred when the siren speakers were mounted on the grill and the cabin windows were closed. Siren noise immediately in front of the ambulance was 122dBA, and 99 to 105dBA at 100 feet from the ambulance when the siren was mounted on the grill. The authors conclude that ambulance siren noise is a potential hazard to drivers and patients. The optimum condition for minimizing noise exposure is obtained by attaching the siren speakers to the grill and keeping the cab windows closed.