Carbon monoxide is a product of incomplete combustion. Because almost all of this gas is produced by motor vehicles, it is considered to have a line rather than a stationary point source. Greatest concentrations of this lethal gas correspond to periods of peak traffic volume and congestion; therefore, there are two daily periods of maxima and minima. Carbon monoxide cannot be detected by sight or smell. For this reason, this gas is especially deadly. During the summer of 1975, a study involving carbon monoxide concentrations at selected sites in Sendai was undertaken in conjunction with an ongoing investigation of urban pollution under the directorship of Professor Toshio Noh of Tohoku University. This study was made possible by a grant from the Japan Society for the Promotion of Science. 5 references, 5 figures, 1 table.