Some aspects of production of gas-liquid bubble systems with very small bubbles (microbubble medium) are discussed. Using photographic measurements and dispersed analysis, parameters of a microbubble medium are determined (bubble mean diameter approximate to 40 mu m). Results of simple hydrodynamic experiments with this medium are described. Measurements of the drag coefficient of a solid ball in the microbubble medium were performed at Reynolds number from 0.1 up to 2.2 x 10(4) and with gas void fraction less than 2.5%. Flow of the microbubble medium in horizontal tubes was investigated under conditions in which the air fraction and the Reynolds number were between 0.0% and 0.7%, and between 10(3) and 2.5 x 10(4), respectively.