The effects of a crude methanol extract, butanol- and chloroform-fractions, and a pure compound, corymine, extracted from the leaves of H. zeylanica on locomotor activity and rearing, pentobarbital-induced sleep, and drug-induced convulsions were studied in mice. The methanol extract dose-dependently decreased rearing without a significant effect on locomotor activity at doses of 15, 60 and 120 mg/kg. It did not significantly prolong the sleeping time but potentiated the convulsions induced by strychnine, but not that by either picrotoxin or pentylenetetrazole, at a dose of 120 mg/kg. The butanol-fraction significantly prolonged sleeping time at a dose of 125 mg/kg but did not affect either of the convulsive drugs. The chloroform fraction prolonged sleeping time at doses of 62.5 and 125 mg/kg and potentiated the convulsions induced by either strychnine or picrotoxin, but not that by pentylenetetrazole, at doses of 15, 30, 60 and 120 mg/kg. Corymine did not significantly prolong sleeping time, but potentiated the convulsions induced by either strychnine or picrotoxin, not by pentylenetetrazole, at doses of 2, 8 and 15 mg/kg. These results suggest that crude alkaloidal extracts of H. zeylanica leaves produce biphasic effects on the central nervous system (CNS), depression and stimulation, while the pure compound, corymine, has a unique central stimulatory effect in mice.