We consider the problem of a, machine shop in which some items are made specially to customor order while other items are made for and subsequently sold from finished goods inventory. It is assumed that both types use the same set of facilities in their manufacture. However, whereas we may have some choice in the timing of replenishment orders which are manufactured for stock, the demands for make-to-order items will not generally permit the same degree of freedom. Consequently when congestion difficulties arise through facility overloading it is often the ‘ stock orders ’ which arc forced to wait. In this case study we present an attempt to measure the relationship between the level of shop congestion and the degree of retardation of stock leadtimes. Clearly if correlation exists, then we might conversely be able to assess maximum loading levels in the light of the stock leadtimes which are deemed to be desirable.