Studies on animals and human subjects have proposed that urban pollutants may cause alterations of cortisol levels. The aim of this study is to evaluate whether police officers exposed to urban pollutants and possible psycho-social stressors could be at risk for alterations on plasma cortisol levels compared to a control group. Plasma cortisol levels were determined in 302 police officers with outdoor activity and administrative workers with indoor activity. The subjects were subdivided into three groups: "A" (non-smokers and non-drinkers), "B" (smokers), and "C" group (drinkers). In male and female subjects of "A" and "C" groups and in female subjects of "B" group the mean cortisol values were significantly higher in police officers compared to controls. The authors hypothesise an effect on plasma cortisol levels in police officers exposed to chemical, physical and possible psycho-social stressors.