A model to describe the growth of Cd1-xZnxTe (CZT) in the multi-tube physical vapour transport (MTPVT) system is presented. This is a novel multi-tube vapour growth system developed at the University of Durham, based on separate vertical source and growth tubes connected by a horizontal optically heated crossmember which incorporates a capillary to regulate the mass flow. Growth takes place on a seed crystal in a semi-open Markov-like arrangement. During crystal growth, the mass transport is directly monitored by in situ measurements of the vapour pressures on the either side of the capillary using optical absorption. This model provides an estimate of the mass transport rate of the source materials CdTe and ZnTe. (C) 2002 Elsevier Science B.V. All rights reserved.