Exhaled breath condensate (EBC) contains many substances, which could help in diagnosis of occupational asthma. The aim of the study is to monitor leukotrienes (LT) and 8-isoprostane from EBC in bronchoprovocation tests with allergens in 47 patients with suspected occupational asthma. Forty-one patients were tested negative. In negative bronchoprovocation tests, no significant differences (P<0.05) were seen between the five measurements during and after the test. In control measurements (without provocation), significant differences were found among four measurements done within 24h for 8-isoprostane (P=0.0138). The relationship between the log transformed ratios of the EBC parameters and FEV(1) was never significant at the 5% level in control measurements, while in negative tests, statistical significance was recorded for LTB(4) (P=0.0299) before and 5h after the test. Six of 47 patients were tested positive. Such a small number of patients did not allow proper statistical analysis and therefore, the results are described separately for each patient.