The relationship between incidence of lung cancer and the volume of traffic as indicated by auto exhaust concentration was examined; the results, though suggestive, did not yield consistent evidence of the association between them. Traffic jams in Nagoya began 15 years ago, a period that may not be long enough to provide definitive data on the incidence of lung cancer. The high standardized mortality ratio (SMR) of lung cancer was observed in cities with a population of less than 1 million and guns (rural areas) along the coast, although those in the metropolitan areas with populations of more than 1 million were average. The SMR did not correlate with various socioeconomic conditions and industrial air pollution. Meteorologic or geologic conditions and ocean currents were not associated with SMR of lung cancer by city and gun. The population of a gun or of some cities was not large enough to be statistically significant, and the mortality rate of lung cancer was not always stable.