A questionnaire survey to assess the effectiveness of the use of the UNFCCC technology information clearing house TT:CLEAR attracted 303 respondents from 81 countries. A large majority (85 per cent) of the survey respondents found the web site useful and relevant to their work, 83 per cent of respondents found the quality of information good or excellent, and more than 70 per cent of respondents indicated that TT:CLEAR was well organized and easy to use, loaded quickly and operated smoothly. Respondents provided many suggestions for future improvement and identified some problems relating to usability of the system as well as its organization, structure and search engine.