Because of fluctuation in levels of industrial air pollution linked to weather and other factors, a joint U.S.-Soviet research team studied differences in the effect of time in exposures of air-breathing animals to controlled varied concentrations of air pollutants. An experimental model environment was used to investigate the effects of nitrogen dioxide, sulfur dioxide, and benzene in the air environment of laboratory animals, with both continuous and intermittent exposures. For intermittent exposures the investigators used amounts of toxic gases whose cumulative total equaled the total in the continuous exposures, and intercalated the intermittent exposures with periods of nonpolluted air. Part 1 of this work deals with the effects of continuous exposure to benzene on the central nervous system and blood. Toxic effects of continuous exposure to various concentrations of benzene were found in these systems. The time-effect relationships could be approximated on a log-log scale by straight lines. Similar results were obtained with sulfur dioxide. Using different parameters to measure toxicity, similar results were obtained with nitrogen dioxide, namely concentration-time relationships that when plotted on a log-log scale gave straight lines.