In this paper we present the results on experimental investigation of the local opposing mixed convection heat transfer in the vertical flat channel with symmetrical heating in a laminar-turbulent transition region. The experiments were performed in airflow (p = 0.1-1.0 MPa) in the range of Re from 1.5 x 10(3) to 6.6 x 10(4) and Gr(q) up to 1 x 10(11) at the limiting condition q(w1) = q(w2) = const. The analysis of the results revealed significant increase in the heat transfer with increasing of air pressure (Gr number). Also sharp increase in heat transfer was noticed in the region with vortex flow in comparison with the turbulent flow region. (C) 2010 Elsevier Ltd. All rights reserved.