The Web offers a powerful tool for knowledge-sharing among small and medium sized enterprises (SMEs). Such online initiatives have, however, frequently been unsuccessful. This paper examines factors motivating SMEs to share knowledge online. It reports data from a telephone survey of 192 SME members of two successful regional business networks comprising members from diverse industries. Although the majority of SMEs actively used the Web in their daily business operations and most were willing to share knowledge face-to-face, this did not translate into willingness to share online. The most significant factors affecting the willingness to share knowledge online were the how many of networks SMEs were involved in, the number of years an SME had been in business, the geographical scope of their operations, and intensity of their use of the web. These findings challenge the commonly-held view that SMEs will automatically share online if the infrastructure is provided.