Inventory control in a Supply chain is crucial for companies desiring to satisfy their customers demands as well as controlling costs. This paper examines specifically supply planning under uncertainties in MRP environments. In literature, many models exist for a random demand, certain of them are described and commented in this paper, also presented are some results for lead time uncertainties. Lead time uncertainty has been ignored in the past, in spite of their significant importance. In particular, a promising research area concerns assembly systems with uncertain lead times, for which the main difficulty comes from the inter-dependence of components inventories. Another promising area, which is also presented, concerns the supply planning under simultaneously demand and lead-time uncertainties, which certainly is of great interest for both the academic and industrial communities.