The objective of the study is to develop an effective and universal approach, based on the theory of Markov chains, to calculate the basic parameters of the steady state regime of complex technological systems for processing granular materials. In particular, we focus on the response of a complex milling system to fluctuations of the feed rate to the system. It is shown that depending on the characteristics of the classifiers the fluctuations can grow unlimitedly, so that the stability of throughputs in the circuit can be lost. (C) 2004 Elsevier B.V. All rights reserved.