The analysis of root extracts from Lonchocarpus montanus A.M.G. Azevedo resulted in the isolation of twenty three compounds chiefly flavonoids of which five (four flavonoids and one benzophenone) are described for the first time. The molecular structures of the new compounds (1-5) were determined through spectral analysis (UV, IR, MS and NMR) as being: 2'-hydroxy-8-(alpha,alpha-dimethylallyl)-2',2'-dimethyl-pyrano-(5',6':3',4')-dibenzoylmethane(1), 2'-methoxy-8-(alpha,alpha-dimethylallyl)-2', 2'- dimethylpyrano(5', 6': 3', 4')-dibenzoylmethane (2), 4'-methoxy-2', 2'- dimethylpyrano-(5', 6':8,7)-flavone (3), 2'-(1-hydroxy-1-methylethyl)- furano-(4',5':8,7)- flavone (4) and [2'-methoxy-furano-(4',5':3',4')- phenyl]phenylmethanone (5). Additionally, fifteen fatty acids were detected through GC- MS analysis of the corresponding methyl esters [(CH3)(2)CH(CH2)(8)COOH and CH3(CH2)(n)COOH (n = 6, 12- 24)]. Quantitative RP- HPLC showed that the most abundant flavonoids in the petroleum ether and dichloromethane extracts were pongamol (19%) and lanceolatine B (8.0%), respectively. In the bioautography assay, the extracts, pongamol ( 9), lanceolatine B (10), isolonchocarpin (14), derriobtusone A (17) and medicarpine ( 18) were active against Staphilococus aureus whereas 9 also against Bacillus subtilis and Cladosporium cladosporioides. Compound 1, 2', 2'-dimethylpyrano-(5', 6':8,7)- flavone (11) and furano-(12', 13':7,8)-4'- methoxy flavone (12) were active against Fusarium oxysporium whereas 11 also against Rhizopus orizae. The extracts, compounds 9, 10, 17 and (E)-7- O- methoxypongamol (23) displayed high toxicity in the brine shrimp lethality assay.793351367