In anticipation of a changeover from the measurement of intoxication through blood sample analysis to the use of breath testers, laboratory tests of a variety of breath testing equipment were performed, and the three best systems were selected for field tests. These were the C.M.I. Intoxilyzer 4011 A, the Intoximeters Inc. Gas Chromatograph Intoximeter Mk. IV, and the Smith and Wesson Breathalyzer 1000. These instruments are all manufactured in the United States and are currently in use there. Police officers were trained as operators and 12 locations were selected for the tests. With 4 examples of each instrument used sequentially in each location, by the end of the 7-month trial period, each police station had used each type of instrument for at least 2 months. During the trial, the calibration of each instrument was checked before a subject was asked to provide breath samples and was also checked daily on a routine basis. A Smith and Wesson Breath Simulator Mk. IIA provided a simulated breath sample using alcohol/water solutions of known concentration to generate vapors of the required alcohol concentration for the checks. Of the 1776 motorists invited to provide breath specimens, 1516 agreed to do so. Of these, 1336 also provided a blood specimen for analysis. Suitable pairs of breath and blood samples were obtained in 991 cases. The results showed that each type of instrument performed well and produced results which were in good agreement with the blood test results. The instruments are described in detail, as are problems encountered with them during the trials; the views of the testers are also presented. Performance data are presented in tabular and graphic form. A reference list and appendixes containing a location map, photos, and additional characteristics of the instruments, and laboratory evaluation information are included. (Author abstract modified.)