Readers of this journal were introduced to the Population Growth Estimation (PGE) experiment in the issue of Spring 1962 . Since then five mimeographed interim reports1 have appeared and two papers have been presented to international conferences [23 ;4]. The experiment is now in its third year and the time has come to report more comprehensively on the findings and experiences of the first two years. We feel the importance of the findings to be so great for the future of this country (and the confidence in their reliability to be sufficiently high) that they should be disclosed. Even if not immediately accepted, the findings will provoke continued enquiries, resulting in eventual acceptance of more generally agreed upon vital rates. Simultaneously, a more comprehensive report in the form of a monograph is being prepared . Opinions of an assertive nature in this article will — it is hoped — be justified more convincingly in the monograph. The monograph will thus enable both the authors and the readers to subject the PGE experiment and its findings to a much more penetrating criticism than the current article. Although this article is a report on the first two years of the experiment, it repeats in broad strokes some of the introductory material available elsewhere. Readers familiar with the experiment will excuse this tendency to ensure that the present article is self contained. Besides discussing certain natural developments arising from the experiment, this paper indicates briefly some evolutionary shifts in our thinking and the consequent changes in the organization and administration of the experiment.