The effects of prednisolone, theophylline or salbutamol treatment were studied on leukocyte numbers in bronchoalveolar lavage (BAL) fluid taken 72 h after ovalbumin challenge in sensitized guinea pigs. Ovalbumin challenge resulted in an approximate 3-fold increase in the number of eosinophils in BAL fluid. This increase was significantly reduced by oral administration of prednisolone (59% inhibition with 10 mg/kg x 2) theophylline (56% with 50 mg/kg x 2) but not by salbutamol (10 mg/kg x 2). A comparison with the bronchodilator potency of the above drugs indicated that in guinea pigs salbutamol appears relatively selective as a bronchodilator, prednisolone is selective as an inhibitor of eosinophilia whilst theophylline displays a balance of both activities.