In the present study, the specific hydrolytic activity of three biocatalysts such as the constitutive mycelium-bound lipase, the induced mycelium-bound lipase and the lyophilized induced supernatant from A. niger MYA 135 was evaluated in both aqueous and organic media. A direct correlation between activity in water and n-hexane was not observed for the same hydrolytic reaction. The n-hexane/water activity ratio (R-O/A) was applied to characterize the activity in organic medium. The three biocatalysts showed R-O/A values higher than 1 for hydrolysis of long-chain fatty acid esters, demonstrating a higher specific hydrolytic activity in organic solvent than in water. A different behavior was observed during hydrolysis of middle-chain fatty acid esters, which was higher in aqueous medium (R-O/A < 1). Transesterifications of different alcohols with various p-nitrophenyl derivatives using all three biocatalysts preparations were also evaluated in n-hexane. For methanolysis and ethanolysis, the constitutive mycelium-bound lipase displayed an interesting preference for C16 substrate (p-nitrophenyl palmitate). The induced mycelium-bound lipase showed high specific transesterification activities in the presence of water-miscible alcohols and middle-chain fatty acid esters (p-nitrophenyl caprate and p-nitrophenyl laurate), being the highest specific transesterification activity (91.4 +/- 1.7 mU/g(dw)) observed in a reaction mixture containing propanol and p-nitrophenyl laurate. Finally, both p-nitrophenyl caprate (C10) and p-nitrophenyl laurate (C12) were preferentially methanolized by the lyophilized induced supernatant, being this lipase activity the most specific biocatalyst preparation under transesterification conditions. A selectivity-based analysis of each lipase preparation toward transesterification or hydrolysis in organic medium was evaluated as well.