One hundred and twents! seven strains of E. coli, isolated from the suckling piglets with diarhea in Taiwan, were used for the sensitivily tests against 15 different kinds of drugs. The results indicated that the strains had a tendency to resist 15 different kinds of drugs. The results indicated thatthe strains had a tendency to resist not only several drugs even to 9 kinds of the tested reagents. Therefore, in the field application, the choice of the effective drugs was rigidly restricted. Furthermore, from approximately a half of the resistant strains, the messengers of R-Plasmids were detected. As they possessed markers for several agents. those plasmids were anticipated to induce a wide spread in the field applications of drugs.