Using R 113 vapor and liquid, behavior of the two-phase mixture level was examined in both cases of bubbling a stagnant liquid column in vertical pipes and bubbling a liquid column to which liquid was supplied as a falling film. The pipe diameters used were 10.0, 14.8, 20.2 and 26.0 mm. The initiation condition of flooding in the latter case was also examined. Observed phenomena were quite similar to those in previous air-water experiments. However, the level fluctuation amplitude and the mixture level swell height in the experiments with the falling film were smaller than those in the air-water experiments. Physical models devised to predict the mixture level height and the flooding velocity under a slug flow condition, which were developed in previous work, were found to reproduce the experimental results well.