Urinary bicarbonate has been considered to be negligible, and the pH of urine to be low (around pH 5.5) for these fifty years. It was, however, found that the contents of bicarbonate and pH of the urine of adult Tokyo citizens (435 adults including 148 males and 287 females) substantially increased. The findings may be correlated with increased inhaled amounts of carbon dioxide which finally causes the increase of urinary excretion of bicarbonate, though evidence that the gas accumulates in the atmosphere of Tokyo due to air pollution has not been directly demonstrated.