The paper describes the implementation of a control strategy for the milling circuit at Buffelsfontein Gold Mining Company Limited.The milling plant is a material flow bottle-neck for the metallurgical operation, therefore the control objectives were based on the requirements of maximum tonnage throughput at a given consistent fineness of grind.The plant comprises three independent milling circuits. The control strategy was implemented on one of these. The milling circuit has a rod mill in open circuit, discharging into a common sump. Six parallel pebble mills operate in closed circuit with the sump, a six-way pulp distributor and independent hydrocyclones. The hydrocyclone overflow streams combine in a common launder feeding a secondary cyclone before discharging the product to the plant thickeners.The control strategy embarked upon is one which aims to maintain a constant circulating load in the milling circuit. The rod mill feed rate is controlled, within certain limits, in order to ensure a constant solids lock-up in the circuit.The optimum value of the circulating load is a complex function of several variables, the state of which is difficult to estimate. The objective followed is thus to use an EVOP technique for finding the circulating load which maximisesthroughput at a given product size.Fineness of the final mill product is controlled by water addition to the distributor. Pebble addition to the mill is controlled by a simple, robust strategy aimed at maximising mill energy consumption. Mill dilution is similarly controlled.Initial results achieved are encouraging and reflect an increase in tonnage milled with improved consistency of grind.The discussion centres around the concept of multivariable control and decoupling using simple heuristic arguments. The control concepts are by no means general or of closed form nature. However, they reflect the advantages of using small computer systems in applying deductive logic to solve complex interacting systems. Comparisons will be drawn between the approach followed in this project and that presented on the non-linear state estimation approach attempted on this milling circuit and reported at the 3rd I.F.A.C. symposium in Montreal under the title ‘Realtime Digital Computer State Estimator for a Hard Rock Milling Circuit’, by G.F. Wyatt-Mair et al.