In order to meet the needs of consumers, manufacturers of milk drinks should undertake improvement work on improving functional properties of those drinks, among other things, by adding pro-biotic bacteria. Those bacteria do not possess any typical ability to ferment milk, but milk fermentation is the process when compounds are formed that decide on sensory qualities of milk drinks, and, first of all, on their smell and taste. The objective of this paper was to determine differences between the profile of volatile compounds in milk drinks fermented by using pro-biotic bacteria and the profile of milk drinks fermented and nonfermented by applying a typical yoghurt culture. The biggest differences in the profile of volatile compounds in the drinks investigated arose due to various types of bacteria cultures applied. The bifidobacterium animalis subsp. lactis and Lactobacillus casei created favourable conditions for acetic acid to form in a significant amount in the product, and this acid increased the differences among sensory properties of the yoghurt and bio-yoghurt studied. Next, significant differences were found in the production volume of volatile compounds in samples fermented using the above bacteria, as well as in non-fermented samples. The Lactobacillus casei bacteria showed a significant biochemical activity. In the fermented milk, these bacteria caused the most intense increase in the content of such compounds as 2-heptanone, 2-pentanone, and ethanol, whereas in the non-fermented milk: ethanol and organic acids, in the fourth week of storing the samples.