Tracer techniques are well-established methods in investigations of a flow process dynamics. The concept of experimental evaluation of residence time distribution (RTD) is widely utilized. There exist advanced methods of RTD function analysis. The methods generally assume the constant flow rate in the system. In this work, we aim to determine the flow parameters for a process under variable flow rate using ordinary tracer data. The experimental study analyzed as an illustration of the method is the tracer experiment carried out on a pilot scale system-packed bed reactor. (c) 2005 Elsevier Ltd. All rights reserved.