Web forums and online communities are becoming increasingly important information sources. While there are significant research works on classification of Web pages, relatively less is known on classification of online discussions. By observing the special nature of user participation in web communities, we propose classification methods based on user participation and text content of online discussions. Support vector machines have been employed in this study to classify and analyze discussions based on content and participation. It is found that the accuracy of using participation as classification features can be very high in certain communities. The use of high-dimensional classifier can be effective in enhancing retrieval and classification of online discussion topics.