The premixed gas flame spreading through an array of large-scale vortices is studied numerically. It is found that the flame speed is a nonmonotonic function of the stirring intensity. At sufficiently low Lewis numbers (Le < 1) the system becomes bistable with a hysteretic transition between possible propagation modes. In the presence of volumetric heat losses the stirring invariably promotes extinction (reduces the flammability limits), provided Le > 1. At Le < 1 this holds only for sufficiently strong stirring, whereas moderate stirring actually expands the flammability limits. At Le > 1 the deficient reactant is fully consumed up to the very quenching point. At Le < 1, prior to the total extinction, part of the deficient reactant escapes the reaction zone and remains unconsumed. (c) 2005 The Combustion Institute. Published by Elsevier Inc. All rights reserved.