Seven coumarin derivatives (imperatorin, heraclenin, xanthotoxin, marmesin, chelepin, oxypeucedanin, esculin) and a furan derivative (nimbolide) were screened on 6 Ames tester strains (TA92, TA94, TA97, TA98, TA100, TA102). The eight compounds are chemicals isolated from three Nigerian medicinal plants:Afraegle paniculata, Clausena anisata, andAzadirachta indica. Different preparations of the former are taken by Nigerians for gut disturbances, and a concoction of the latter called “Agbo” is taken as an antimalarial.