Prior to the nationwide diffusion of a new technology, evidence must be assembled to demonstrate that a new technology is, in the terminology of WHO, appropriate. Not everything that is new in health technology is good; not all that is good is needed. It is by no means unethical to demand adequate assessment of new technology before it is diffused. On the contrary, it is unethical to squander resources on hazardous and uneffective treatment. Of the methods available for assessment, the randomized clinical trial is among the most valuable. Randomized clinical trials cannot, however, solve all problems. Speed is a critical element. It is not ethical to permit excessive delay. Balanced, relevant, and informative studies must be conducted as quickly as possible and with a maximum of international collaboration. WHO has a valuable role to play in advising on, coordinating, supporting, and disseminating the findings of such studies.