Antimutagenicity, antioxidant activity, cytotoxicity and antimicrobial activity of methanol extracts of some edible plants in Thailand were evaluated. Some plant extracts exhibited definite bioactivities. Micromelum minutum (Rutaceae) showed the highest antimutagenicity among 118 samples, and it contained a carbazole alkaloid, mahanine, as an active principle. Mahanine showed a wide variety of bioactivities, particularly antimutagenicity, and toxicity against tumor cell lines such as HL-60. Rhizomes of fingerroot (Boesenbergia pandurate), a common Thai spice belonging to the ginger family, showed a remarkable antimutagenicity and six active constituents were isolated and identified. Twigs, fruits and flowers of Oroxylum indicum (Bignoniaceae) contained a high concentration of baicalein which is a flavonoid exhibiting antimutagenic and antibacterial activities. Extract of Azadirachta indica (neem) inhibited growth of gram-positive bacteria, proliferation of tumor cell lines, and mutagenesis induced by heterocyclic amines. These studies would be a good basis for an inventory of indigenous plants and minor crops based on bioactivities.