This study concerns boiling incipience of highly wetting liquids (n-pentane), in transient conditions, in horizontal confined space between a vertical heating cylinder and a disk. The two controlled parameters were the heat flux, ranging from 50 to 200 kW m(-2) and the thickness of the liquid in the confined space, ranging from 0 to 240 mum. Experiments were conducted with both smooth and porous disks. The results suggest that in the porous-disk configuration, boiling could appear on the non-heated wall. (C) 2003 Elsevier Ltd. All rights reserved.