The properties of an organic phase (Hostarex (20% w/w) in oleylalcohol) for extractive and pertractive fermentative production of butyric acid by Clostridium butyricum were investigated and the ability of this organic phase to be used in the fermentation process was established. The distribution coefficient of butyric acid between water and the organic phase could be increased up to 13 in diluted solutions but decreased to 3.0 with an increase of pH up to 5.2 (pH of the fermentation process). The kinetics of direct extraction of butyric acid during both extraction and pertraction were two and three times, respectively higher than the reverse processes. Reverse stripping was faster, but remained slower than direct stripping. These results demonstrated that both extraction and pertraction could be successfully joined with fermentation. An increase of total butyric acid concentration, from 7.3 g l(-1) in the control to 10.0 g l(-1) in extractive fermentation and to 20.0 g l(-1) in pertractive fermentation and concurrent increases of yield of butyric acid from 0.24 g g(-1) in the control up to 0.30 g g(-1) in pertractive fermentation, showed the great possibility of successful integration of these separation processes with fermentative production of butyric acid by C. butyricum.