The possibility of using a model reference adaptive control scheme to improve the control of a rotary solids drier is examined; in this process time delay makes efficient and accurate control difficult when conventional feed back control is used. The choice of realistic performance criterion is discussed which is suitable for computation by a digital computer. It is shown that effective control can be achieved by optimizing the performance of a model representing the part of the process without the time delay, and storing the optimum control signal for the duration of the time delay before applying it to the process. Various optimizing procedures are presented and it is shown that a particular iterative procedure gives the best results.The problem of the drift which will occur if the model does not accurately match the process is discussed and it is suggested that this may be overcome by using a direct feedback loop to trim the process output. This is part of an integrated research programme in the control of solid material processes and some directions for future work are indicated.