Experimental and human studies have demonstrated that dermal exposure to isocyanates is a significant risk factor for sensitisation to isocyanates. Recent occupational medicine studies demonstrated the link between exposure to isocyanates, skin sensitization and astma. The aim of the study was to evaluate the nitro-oxidative stress markers in human subjects with occupational exposure to isocyanates and without clinical and functional manifestations of occupational asthma. Workers occupationally exposed daily for two weeks to isocyanates and without asthma (n = 70, M/F =23/47) were compared to a control group of healthy individuals (n=50, M/F=25/25) not exposed to isocyanates or other toxic agents. Nitro-oxidative stress was evaluated by measuring serum nitrotyrosine (3NT), total nitrites and nitrates (NOx), total oxidative status (TOS), total antioxidant reactivity (TAR) and oxidative stress index (OSI). Tissue injury was appreciated by measuring serum MMP-9. Values are means ± S.E.M., compared by ANOVA. In subjects occupationally exposed to isocyanates the systemic levels of NOx (85,11±5,46 vs. control 42,46±6,12μmol/L, p<0.05), 3NT(358,96±52,04 vs. control 161,72±14,48 µmol/l, p<0.05) TOS (13,95± 1,22 vs. control 11,95±0,29 μmol echivalent H2O2/L, p<0.05), OSI (3,71±0,32 vs. control 1,23±0,0005, p<0.05) and MMP-9 (13,55±1,99 vs. control 10,34±1,24 ng/ml, p<0.05) were significantly increased, and TAC (0,37±0,08 vs. control 1,23±0,05 mmol echivalent trolox/L, p<0.05) was lower than in healthy subjects. The nitro-oxidative stress parameters did correlate with serum MMP-9 level. These data suggest that occupational exposure to isocyanates is associated with systemic nitro-oxidative stress before onset of clinical signs of occupational asthma. 2. Serum nitro-oxidative stress tests correlate with MMP-9. 3. These tests may be recommended for early diagnosis in hypersensitivity to isocyanates.