From the view points of safety and efficacy of sodium guaiazulene-3-sulfonate (GAS) after oral cavity administration, the absorption behavior of GAS was investigated in rats and rabbits and following results were obtained. 1) GAS was absorbed not from oral cavity but from nasal cavity in rats and rabbits. 2) The in situ perfusion experiments revealed the existence of dose-dependent specific absorption mechanism in the rat small intestine. 3) GAS was absorbed from neither the rat stomach nor the rectum. These facts reveal that GAS transfers into the systemic circulation only through the small intestine after the clinical application to the oral cavity. And these absorption characteristics of GAS are suited for its direct action on the inflamed oral mucosa. When GAS is administered into the oral cavity, the safety is at least the same as that obtained after oral administration.