The aim of our study is to estimate if the occupational exposure to formaldehyde can cause alterations of leukocytes plasma values in health care workers employed in a big hospital compared to a control group. We studied employees in operating rooms and laboratories of Pathological Anatomy, Molecular Biology, Molecular Neurobiology, Parasitology and Experimental Oncology (exposed to formaldehyde) and employees of the Department of Internal Medicine (not exposed). The sample studied was composed of 86 workers exposed to formaldehyde and 86 workers not exposed. All subjects underwent a clinical-anamnaestic examination and for all subjects were measured the following values: total white blood cells, lymphocytes, monocytes and granulocytes (eosinophils, basophils, neutrophils). Statistical analysis of data was based on calculation of the mean, standard deviation and the distribution into classes according to the nature of each variable. Differences were considered significant when p was < 0.05. The mean and the distribution of values of the white blood cells, lymphocytes, monocytes and eosinophils were significantly higher in male subjects exposed to formaldehyde compared to not-exposed. Not significant differences were found in female subjects exposed compared to not exposed. The results underline the importance of a careful risk assessment of workers exposed to formaldehyde and the use of appropriate preventive measures. The health care trained and informed about the risks he is exposed to should observe good standards of behavior and, where it is not possible to use alternative materials, the indoor concentrations of formaldehyde should never exceed occupational limit values.