A phytochemical investigation of the stems and roots of Mucuna aterrima led to the isolation of the following constituents with nematicidal activity: KNO + NaNO, a mixture of fatty acids, a mixture of triacylglycerols, -sitosterol, stigmasterol, daucosterol, stigmasterol D-glycoside, allantoin. An in vitro bioassay was carried out, and at the concentration of 5 g ml the percentage of mortality caused by the compounds varied from 2.1% to 74.4% in the case of M. incognita and 0% to 74.2% for H. glycines. The non-essential amino acid L-3,4-dihydroxyphenylalanine (L-Dopa), present at 6-9% in the seeds of Mucuna spp. was tested for the first time against the phytonematodes M. incognita and H. glycines, and the LC was 21 g ml and 0.17 g ml respectively.