This paper analyzes instant knowledge sharing among customer support agents. Customer support agents effectively exchange useful information through electronic mail and electronic bulletin board services. Empirical analyses have taught us that the direct use of electronic mail is the key towards instant knowledge sharing in busy organizations like high-tech product customer support organizations. The authors have developed “Interaction Viewer”, an instant CBR tool that runs with commercial electronic mail management systems such as Microsoft Outlook Express. The tool analyzes the relations among electronic mail messages by tracing the body texts and extracting quotation descriptions inserted in the bodies. A pair of a question mail message and its answer mail message is integrated into a case. Because all mail messages are automatically modified into cases and mail folders are transformed into a case base, instant knowledge sharing is easily achieved. Although the case retrieval performance is not as good as more integrated CBR systems, the easy-to-adopt feature of the approach should be welcome by busy organizations. It should also be welcome by marketing divisions to analyze various customers opinions.