High-speed video recording was carried out of annular flow of steam-water mixtures in an internally heated annulus test section. The heated section was 0.32 m long and made of stainless steel. The equivalent diameter of the channel was 12.9 mm. The results demonstrated the interaction between disturbance waves in the liquid film and the activity of nucleation sites. (C) 2003 Elsevier Ltd. All rights reserved.