This paper deals with the theory of two-phase laminar flow in a heated microchannels. The main objective of the work is to study the thermohydrodynamic characteristics of a two-phase capillary flow with phase change at the meniscus. A quasi-one-dimensional model is proposed for such a flow. It takes into account the principal characteristics of the phenomenon, namely, the effects of the inertia, pressure, gravity, friction forces and capillary pressure due to the curvature of the interface surface, as well as the thermal and dynamical interactions of the liquid and vapor phases. To describe the flow outside of the meniscus, in the domains of the pure liquid or vapor, the one-dimensional mass, momentum and energy equations are used. The possible states of the flow are considered, and the domains of steady and unsteady states are outlined. An equation for stationary two-phase flow regimes in heated microchannel is derived. This equation is applied to classify the operating parameters, corresponding to various types of flow. (C) 2002 Elsevier Science Ltd. All rights reserved.