The plant Mucuna pruriens is used extensively in Indian systems of medicine for its aphrodisiac property and in cases of nervous and sexual debility. Recently, several indolealkylamines were isolated from various parts of the plant. Preliminary pharmacological studies showed that the total indole-alkaylamines produced central nervous system stimulation. In the present study the total indolealkylamines were investigated for their hallucinogenic activity. They produced marked behavioural changes, antagonised pentobarbitone induced 'hypnosis, inhibited reserpine induced ptosis, hypothermia and sedation, reduced chlorpromazine induced catatonia and enhanced amphetamine toxicity in aggregated rats. The data made available suggests that the clinical use of the plant is due to these hallucinogenic indoles.