The semi-input-output method, as presented by Tinbergen , is designed solely for the evaluation of investment projects. It tells us, given the criterion used, which sectors or industries should get priority in a development plan. The method does not tell us to what extent the production of an attractive industry should be increased. To solve this problem we need a planning model. The main aim of the present note is to show the possibility of formulating a planning model based on the semi-input-output method. As such, the present paper should be considered as an extension of the article by Tinbergen. Before coming to our main subject however, I would like to make two comments on the paper by Tinbergen .