Appropriateness and necessity research of various procedures in medicine may be the most complex field of innovation in healthcare and technology assessment. Nevertheless, the appropriateness of the indication of any medical intervention is probably more important than the outcome since even ideal quality components of structures, processes and outcomes become irrelevant without a proper indication. The first part of our appropriateness initiative in interventional cardiology and gynecology was to formulate guidelines. To define the appropriateness for coronary angiography, coronary revascularization and hysterectomy, literature-based consensus methods were used. The second part was to disseminate the guidelines in a user-friendly manner via the Internet. Therefore, we relied on a system-driven query facility for propositional (experts) rules. The next part of the appropriateness initiative may be a user-friendly Internet-based data collection system to validate the national accepted guidelines. Most important may be that only data that is needed can be collected using a refined database technology. The described Second Opinion System can be found under: http:sos.inf.ethz.ch. Research on indications with data on clinical outcome may open new opportunities to validate indication guidelines using Internet/database technology for data analysis and browsing of decision graphs concerning clinical decision-making. This new technology facilitates the evaluation of appropriateness and necessity criteria in combination with clinical outcomes.