Detailed observations were made for slug flow in an upward to downward pipeline configuration with 13 capacitance sensors. The results presented in this study are based on four typical tests, which demonstrate the phenomena encountered in slug dissipation. In downward flow, slug frequency decreases with different extent at different flow rates. There is a reduction of slug length after the turning over from upward to downward flow. However, the slug tends to recover its stable length in further downstream development, except for flow that quickly becomes stratified. Growth of the slug length is accomplished by picking up liquid left by the downstream dissipating slug before being fully absorbed by the liquid film. [S0195-0738(00)00503-3].