The antimicrobial activities of 24 natural coumarins on the nine strains of bacterium and two strains of fungi have examined by using the agar-dilution-plate method, amoung them, only four coumarins, namely, demethylsuberosin, limettin, nordentatin and (-)-heraclenin, showed significant effects, and the most attractive fact was that nordentatin, with very low concentration level (10 ppm) still showed completely inhibitory effects against most of the bacterial strains being tested. 本報告以平碟稀釋法(Agar-dilution plate method)測定24種天然香豆素對九種細菌和二種黴菌之抗菌能力，發現其中的四種，即demethylsuberosin, limettin, nordentatin及(－)-heraclenin具有抗菌力。Demethylsuberosin在500ppm之濃度下對黴菌有完全之抑制力，而在100ppm之濃度時，則對大部份之細菌有抑制力Limettin在200ppm之濃度下對部份革蘭氏陰性細菌有效，(－)-Heraclenin在500ppm之濃度下，對E.coli病原性之pneumococlus及Pseudomonas aerugenosa有效。最令人注意的是Nordentatin，它在10ppm之濃度下，仍對大部份之實驗細菌有抗菌力。
