Data on exhaust emissions were obtained from a group of 1970 model-year vehicles operating over a range of ambient temperatures. The work is providing a baseline against which current-production vehicles can be compared, thus enabling a more complete assessment of automotive emissions reduction achievements.The vehicle fleet represented the 1970 model-year nationwide mix. The 25 cars were tested at 25°, 50°, 75°, and 100° F over the Environmental Protection Agency urban Federal test procedure, highway fuel economy test, and New York City driving cycles.Both temperature and driving cycle were found to have significant effects on exhaust emissions. The conditions which yielded the greatest adverse effects on emissions were: 1) low temperature--urban driving cycle, and 2) high temperature--New York City driving cycle. The data also indicate that the use of air conditioners causes increased emission levels.