We will consider an economy with two goods where stocks at any time are transformed into another configuration of stocks one period later via the Cobb-Douglas production functions. Stocks available at the beginning of a period will serve as inputs; stocks available at the end of the period will equal initial stocks plus flow-output minus depreciation during the period. For simplicity, we will call the end-of-period stocks the outputs of the period. If the life of each good is one period, then Cobb-Douglas production functions will have the usual interpretation. If any good is durable beyond one period, we assume the Cobb-Douglas functions are engineering transformation functions of one stock-vector into another, taking account of current output, depreciation and replacement. (Such transformation functions have been used in Dorfman, Samuelson and Solow1, Chapter 12.) Our purpose is to maximize the value of terminal stocks in a T-period program. We will show, that the turnpike theorem holds in a very strong sense if the optimum program results in specialisation at the terminal date. If the optimum paths of stocks do not specialize in one commodity, the turnpike theorem will not hold; rather an optimum path will eventually stay away from the von Neumann balanced growth path2 by a distance dependent on the given terminal prices.