Effects of ginsenoside Rg1 (Rg1), a major component of panax ginseng, on modulation of ingestive behavior were investigated. No direct effect was observed on food intake after 10 microliters infusion of 1.0, 2.0, 4.0 or 8.0 mM Rg1 into the rat third ventricle for 10 min. Continuous osmotic infusion of 4.0 mM Rg1 at a rate of 0.966 microliter/h into the third ventricle prevented feeding suppression caused by surgical procedure to implant an osmotic minipump. Continuous infusion of Rg1 attenuated anorexia, increased water intake, and decreased ambulation, that were produced by elevation of environmental temperature from 21 degrees C to 30 degrees C. Consequently, rats maintained body weight and rectal temperature unchanged. The results indicate that sustained central administration of Rg1 may relieve anorexia caused by implantation surgery or by a heated environment.