We established a sensitive and accurate method for screening of anti-adenovirus agents using the 3-(4,5-dimetylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. MKN-28 cells, which are well-differentiated stomach adenocarcinoma cells, were used for adenovirus (ADV) infection and examined for the anti-ADV activities of several established anti-herpes virus agents. ADV-11 is the causative agent of respiratory and urinary infections. It frequently causes hemorrhagic cystitis in immunocompromised hosts. One laboratory strain and 4 clinical isolates of ADV-11 were examined, and found susceptible (in order of decreasing activity) to 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (S-2242), (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine[(S)-HPMPA ], and (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine[(S)-HPMPC++ +]. On the other hand, ganciclovir and iododeoxyuridine were only weakly effective and dextran sulfate was ineffective. Our findings indicate that the MTT assay using MKN-28 cells is applicable to anti-ADV screening. The anti-ADV activity of (S)-HPMPA and (S)-HPMPC was confirmed, and, furthermore, S-2242 emerged as a highly potent and selective inhibitor of ADV-11.