[Declaration of Helsinki: its vicissitudes during the last five years]

The Declaration of Helsinki is one of the major ethical guidelines for conducting clinical research. Along its existence it has been modified on diverse occasions, the latest one in October 2000. The objective of this article is to carry out a revision of the discussions that were taken up at this latest modification and the debates raised since its promulgation which still continue, fundamentally in relation to the use of placebo in pharmacological clinical investigation. This includes a revision of the most outstanding articles and of the opinions of the participants in the discussions that have been published in the last five years. The scientists' arguments in favor or against the use of placebo are pointed out. We consider that it is difficult to find simple answers to the questions raised by the use of placebo in clinical trials both in developed countries and in countries under development and that the Declaration of Helsinki continues to constitute a guide of ethical ideal which all those involved in clinical research should try to take into consideration.