The lead content of soils along Chicago's two expressways, the Chicago Loop-terminal Expressway and the Eisenhower Expressway, have been determined in various seasons of the year and at various distances from the roadway. The concentration of lead in soils along the Chicago Loop-terminal Expressway and adjoining city streets show positive correlation (correlation coefficient = 0.988) with the average traffic volume near the sampling sites during the same season. The levels of lead in soils along the Eisenhower Expressway, at the same site, vary with the season; the lead levels are the least during fall and winter and they increase during spring and attain peak values during summer. This seasonal variation in the lead levels is similar to the seasonal variations in average monthly traffic volumes on the expressway. The soil contains as much as 7,600 parts per million of lead (micrograms per gram of dried soil) up to 45 feet and 900 parts per million up to 150 feet from the Eisenhower Expressway. There is a need to investigate the contamination of human beings that live or work in buildings within these distances from the expressways and wider buffer zones need to be provided along future expressways.