Human viral infections are important health problem worldwide. Although much effort has been made, antiviral drugs, because of the unique properties of viruses, are relatively fewer in number and possess relatively narrow spectrum of activities as compared with antibiotics. Moreover, efficacy, drug resistance and side effect are the problems of antiviral drugs in clinical uses. Thus, it is necessary to develop new, effective and safe antiviral drug. / Thirty-seven medicinal herbs, which were collected from Guangdong province or the Hong Kong region, were selected to screen for their antiviral activities against HSV-1 and/or RSV in vitro using a cytopathic effect (CPE) reduction assay. The selection of the herbs was mainly based on their traditional use in the treatment of human infectious diseases of the skin and respiratory tract. / Three of 37 medicinal herbs, Agrimonia pilosa, Pithecellobium clypearia, and Punica granatum, showed anti-HSV-1 activity, which was possibly contributed from polyphenolic compounds in the herbal extracts. Six of 21 medicinal herbs, Blumea laciniata, Elephantopus scaber, Laggera pterodonta, Mussaenda pubescens, Schefflera heptaphylla, and Scutellaria indica, exhibited potent anti-RSV activity with 50% inhibition concentrations (IC50) ranging from 12.5 to 32 mug/ml, and the selective indices (SI) ranging from 11.2 to 40. Moreover, the anti-RSV SI values of Laggera pterodonta and Schefflera heptaphylla were found to be higher than that of ribavirin. Finally, Schefflera heptaphylla having the highest anti-RSV SI value among the active herbs was subjected to further study its antiviral activity. (Abstract shortened by UMI.) / Traditional herbal medicines have been used for a long time in the treatment of human infectious diseases in many countries, including China. Antiviral screening has shown that quite a few medicinal herbs distributed in various regions of the world possess significant antiviral activities with no or limited adverse effects, and many naturally occurring compounds exhibit antiviral activity in vitro and/or in vivo. In the present study, our objectives are to (1) screen for potential antiviral agents from selected herbal medicines traditionally used in southern China, (2) isolate and characterize the antiviral constituents from the most active herb, and (3) probe possible antiviral modes of action of the active compounds. The viruses used in the present study included respiratory syncytial virus (RSV), herpes simplex virus type 1 (HSV-1), influenza A virus (Flu A), and coxsackie B3 virus (Cox B3). However, the present study mainly focused on searching for anti-RSV and anti-HSV-1 agents from selected Chinese herbal medicines. / Li Yaolan. / "October 2004." / Source: Dissertation Abstracts International, Volume: 66-07, Section: B, page: 3506. / Supervisors: Vincent V. E. C. Ooi; Paul P. H. But. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 160-178). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.