We have demonstrated that beta-lipotropin is a precursor molecule and that during its maturation, it gives rise to beta-endorphin. This model is similar to proinsulin, proparathyroid hormone and proglucagon models. Since beta-endorphin is also found in the hypothalamus, one can foresee that its biosynthesis will be similar if not identical. It is then conceivable to believe that the other hypothalamic factors are issued from larger precursor molecules. When this will be shown, and well established, studies on their control mechanism will be much easier.