The oxidant measurements available between 1964 and 1973 at the six CAMP sites (Chicago, Cincinnati, Denver, Philadelphia, St. Louis, and Washington, D. C.) have been evaluated. Elevated oxidant concentrations have been characterized by season of the year, hour of the day, Sunday compared to weekdays, sampling site, trend with time. Differences in results among the CAMP sites can be associated with effects of altitude, local climatology, and chemical characteristics. With the exception of Chicago, a large downward trend in oxidant concentrations has been occurring at CAMP sites. However, there also are experimental results indicating that the factors responsible for this downward trend in central city locations may not be causing a proportional downward trend at suburban sites within urban areas or downwind sites outside urban areas. These CAMP results are consistent with other results obtained elsewhere in the United States. However, the present experimental results appear inadequate to permit proper optimization of control strategies. Adequate attention to these problems is urgently needed in view of their implications, not only with respect to air standards, but to transportation controls, land use, and energy policy.