Cigarette-derived toxic substances are inhaled along with the nicotine that is absorbed to satisfy the smoker's physical demand. Therefore, serum cotinine, a metabolite of nicotine, may be considered to be an indirect marker of absorption of the other toxic substances from smoking. However, few studies have examined factors related to serum cotinine concentrations in natural settings. The authors, therefore, have studied relations among patterns of smoking behavior and serum cotinine concentrations of community residents. Subjects were 60 smoking men living in the town of Yamasaki, Hyogo Prefecture, Japan. Number of daily cigarettes, depth of inhalation, hours from the last cigarette smoked and the total nicotine tolerance score were significantly, while neither nicotine-yields nor butt length of a discarded cigarette was correlated with serum cotinine concentrations. Multiple regression analysis confirmed that depth of inhalation and hours from the last cigarette smoked were independently significant. This finding suggests that attention only to self-reported daily number of cigarettes smoked may not be sufficient to detect smokers who are actually at high risk. Healthcare workers should also pay attention to smokers' patterns of smoking, particularly depth of inhalation.