An objective approach for monitoring the treatment of acute pulmonary exacerbation in cystic fibrosis was evaluated. Eleven biochemical markers of inflammation (erythrocyte sedimentation rate, neutrophil count, C-reactive protein, alpha-1 antitrypsin, haptoglobin, ceruloplasmin, fibronectin, alpha-1 glycoprotein, alpha-2 macroglobulin, C3, granulocyte elastase and anti-Pseudomonas IgG) were measured in blood serum and plasma from 46 cystic fibrosis patients with chronic Pseudomonas aeruginosa colonization before and after treatment. The overall outcome in each patient was evaluated by means of a pondered sum of clinical, chest X-ray and lung function scores. Biochemical markers were related to the overall clinical improvement: haptoglobin, ceruloplasmin, fibronectin and alpha-1 glycoprotein showed a good sensitivity (64-70%), specificity (60-70%) and positive predictive value (86-89%). Granulocyte elastase showed a similar sensitivity (67%) and positive predictive value (85%) but a lower specificity (33%). The negative predictive value was generally poor (32-39%). Our data suggest that the combined measurement of some markers of inflammation and of conventional clinical parameters, may help in evaluating the efficacy of anti-infective treatment in cystic fibrosis.