Objectives: Silica is one of the most documented workplace contaminants. Long-term occupational exposure to silica is associated with an increased risk for respiratory diseases such as silicosis, tuberculosis, chronic bronchitis, chronic obstructive pulmonary disease and lung cancer. Furthermore, a variety of immune-dysfunction-related diseases has been reported in silicotic individuals. Preliminary studies indicating enhanced levels of autoantibodies and several cytokines reflect an involvement of the immune system in the pathogenesis of silicosis and resulting complications. As an early and valuable biomarker of cellular immunity, neopterin is a low-molecular-mass compound belonging to the class of pteridines. It is produced by guanosine triphosphate via interferon-gamma, following the activation of T cells. The aim of the present study was to observe the alteration of neopterin in silica exposure, and also to show whether screening of neopterin levels may be of use for assessment of occupational exposure to silica. Methods: In this study, serum and urinary neopterin levels, both in silica-expo sed workers (n = 22) and healthy volunteers (n = 20), were investigated by ELISA, spectrophotometry and HPLC techniques. Results: Serum neopterin levels of control and exposed groups were measured as 5.98 +/- 0.44 and 7.86 +/- 1.97 nmol/l, respectively (P < 0.05). Urinary neopterin levels were also increased in the exposed group: 97.60 +/- 41.42 mu mol/mol creatinine for controls and 165.59 +/- 78.20 mu mol/mol creatinine for workers (P < 0.05). At the same time, the correlation between urinary neopterin levels, serum neopterin concentration and working years, smoking status, some complaints, and silica status in the working atmosphere were evaluated. Conclusions: Our findings suggest that the following up of neopterin levels may have diagnostic value in silica-related diseases such as silicosis. Moreover, its biological monitoring should be performed in workplaces for clinical diagnosis and prognosis.