Pharmacological effects of brovanexine hydrochloride (BR-222), a new expectorant, on the respiratory tract system was studied in comparison with that of bromhexine hydrochloride. 1. When doses ranging from 5 to 40 mg/kg of BR-222 were given orally (p.o.) or intraduodenally (i.d.) to rats, rabbits and dogs, it caused a significant increase in the output volume of respiratory tract fluid (RTF). It was almost as potent as bromhexine, but its pattern of increasing RTF was different from that of bromhexine. The increase in the serous ingredient of RTF after BR-222 administration seemed to be more remarkable than that after bromhexine treatment, though both drugs had no influences on the component ratio of glucose or protein in the RTF of dogs. 2. BR-222 at 10 and 20 mg/kg (i.d.) showed a tendency to reduce the viscosity of RTF in anesthetized dogs and so did bromhexine. A dose of 10 mg/kg (i.d.) of BR-222 also showed a tendency to reduce the viscosity of sputum obtained from the SO2-exposed rabbits. 3. A dose of 6 mg/kg (i.m.) of BR-222 caused a significant increase in the mucociliary transport rate in unanesthetized pigeons; in contrast with this, bromhexine caused a slight decrease. 4. Both drugs given orally showed no antitussive effects when examined by the "coughing dog" method.