The aim of this work is to evaluate both the toxic effect of different organic media on the stereospecific oxidation of 2-methyl-1,3-propanediol to R-(-)-beta-hydroxyisobutyric (HIBA) in two-phase systems and the extraction ability and selectivity of these non-water miscible phases. Apart from traditional, solvents, specific organic acid-complexing carriers like TOPO, TOA and Aliquat 336 dissolved in different diluents have been studied. Special interest has been focused on the effect of the concentration of the organic phase extractants and the pH of the aqueous phase on the extraction system. TOPO dissolved in isooctane enabled higher K-p values at lower concentrations to be attained and resulted in lower toxicity, but its extractive capacity is strongly dependent on the pH. Our results suggest that using a compromise pH value between optimum for bioconversion and extraction, TOPO dissolved in isooctane can be successfully used as an extractive phase for HIBA production in a two-phase system.