This article addresses the effectiveness of search reformulation using query refinement mechanisms on the Internet. Cognitive load was measured using a secondary digit-monitoring task. The load was found to be lower when using the refinement mechanisms than when perusing document summaries - suggesting that the development of refinement mechanisms can make Internet searching easier. Two refinement mechanisms, one based on statistical term co-occurrence and the other on a shallow natural language parsing technique were tested. No difference in load was found, possibly because of the limited time that subjects spent in the refinement process.