Bacterial endotoxins are seen to possess strong proinflammatory activities. These substances may intensify inflammation in the airways of patients with chronic obstructive pulmonary disease (COPD) and asthma by facilitating release of various mediators from different types of cells. Sulfidoleukotrienes (sLT) cause bronchoconstriction, increase vascular permeability and stimulate mucous secretion. The aim of our study was to evaluate sLT release from peripheral blood leukocytes stimulated by Klebsiella pneumoniae lipopolysaccharide (LPS) and obtained from COPD and asthma patients. Nineteen subjects with mild or moderate stable bronchial asthma, nine patients with COPD and 10 healthy controls entered the study. Cellular allergen stimulation test (CAST)-ELISA test was performed using Bühlmann Laboratories AG kits to determine sLT production. The differences between atopic (462.57 SD = 215.89 pg/ml) and nonatopic (474.25 SD = 158.02 pg/ml) asthmatics in comparison to healthy controls (191.55 SD = 53.2 pg/ml) were statistically significant (p < 0.005) upon LPS stimulation at the concentration of 10 micrograms/ml. At lower LPS concentration (1 microgram/ml) the difference was statistically significant only between nonatopic asthmatics and healthy subjects (p < 0.02). In the COPD group the sLT production in either LPS concentration was higher than in the controls but the difference was not significant. We suppose that leukocytes obtained from asthmatics and COPD patients are more susceptible to LPS than these cells from healthy individuals. An increased sLT production upon LPS stimulation during respiratory bacterial infection may intensify inflammation, bronchoconstriction and increase nonspecific bronchial hyperreactivity.