Aim of the study is to evaluate whether occupational exposure to low doses of pollutants present in the air of the city selected for the study could cause alterations in peripheral blood counts in workers of the Municipal Police with outdoor tasks vs workers with indoor tasks. 279 non smoker males were enrolled and divided on the basis of their different kind of task. The dosage of air pollutants was carried out through the use of personal air samplers on a representative group of workers. Data obtained were subject to statistical evaluation consisting of Homogeneity of variance test, ANOVA univariate test with post hoc Bonferroni correction, Jonckheere-Terpstra test and multiple linear regression analysis. The differences were considered statistically significant when p values were lower than 0.05. Mean levels of RBC, HB, MCHC, WBC and neutrophil cells were significantly higher in traffic policemen and police drivers compared to controls (workers with indoor tasks). Mean levels of MCV, MCH and lymphocytes were significantly lower in traffic policemen and police drivers compared to controls. These results were confirmed by Multiple linear regression test and Jonckheere-Terpstra test. The results suggest that prolonged occupational exposure to low doses of traffic pollutants can alter some lines of the hematopoietic system in exposed workers.