Theophylline, for many years used as a bronchodilatator, is also known to have some anti-inflammatory properties. The aim of this study was to investigate the effect of theophylline on random locomotion and chemotaxis of neutrophils and lymphocytes from 12 patients with mild bronchial asthma and 12 healthy volunteers. fMLP in concentration 10(-8) M was used as a chemoattractant. The experiment was performed using the modified Boyden method. The cells were incubated with theophylline in therapeutic concentrations (from 5 to 20 micrograms/ml) at 37 degrees C for 30 minutes. Motility of neutrophils and lymphocytes was determined as the migration distance of the cell leading front inside the filter (micron). We found no statistically significant differences in both spontaneous and fMLP-stimulated cell motility between asthmatics and healthy subjects. fMLP-stimulated chemotaxis was significantly inhibited after neutrophil preincubation with theophylline in therapeutic concentrations (5-20 micrograms/ml) in both groups. Random locomotion of lymphocytes was slightly but significantly higher in healthy subjects comparing to asthmatics. Preincubation with theophylline at concentrations 10 to 20 micrograms/ml resulted in significant inhibition of fMLP-stimulated chemotaxis in both groups. Our data show the inhibitory action of theophylline on fMLP-induced chemotaxis of both neutrophils and lymphocytes indicating the anti-inflammatory activity of the drug.