We have designed and developed a knowledge-based decision support system using World Wide Web technology. The system uses both rule-based and hypertext knowledge to give support in clinical medicine. We use Arden Syntax for representing rule-based knowledge and HTML for representing hypertext documents. The two representations are integrated to provide extended explanation to the advice produced by the Arden Syntax rules and to find hypertext documents relevant to a specific question and to a specific patient. This way we believe that the usability of decision-support systems can be enhanced.