Voided urines of 53,000 white and 9,300 black cigarette smokers and nonsmokers were studied. Proteinuria was found to be commoner in smokers of both races and sexes. Heavy smokers showed proteinuria more frequently than light smokers. Of eight possible explanatory variables, one, alcohol consumption history, showed some interrelationship in that the smoking status-proteinuria association disappeared among heavy drinkers. Stopping smoking was not associated with a relative decline in proteinuria prevalence. Proteinuria associated with smoking did not appear to be indicative of more serious renal disease. There was a smoker-nonsmoker difference in urine glucose response to oral glucose challenge, apparently explained by higher average 1 -hour serum glucose values for smokers, of unknown mechanism but partially explained by differences in alcohol usage. Hematuria, bacteriuria, and high urine acidity tended to be more prevalent in smokers, though these relationships were not consistently significant.