The main objective of this work was to investigate the biotransformations of (-)alpha-pinene, (-)beta-pinene, and (+) limonene by Aspergillus niger ATCC 9642. The culture conditions involved -concentration of cosolvent (EtOH), substrate applied, and sequential addition of substrates - were investigated. Adaptation of the precultures with small amounts of substrate was also studied. The experiments were performed in conical flasks with liquid cultures. This strain of A. niger was able to convert only (-)beta-pinene into alpha-terpineol. An optimum conversion of (-)beta-pinene into alpha-terpineol of about 4% was obtained when the substrate was applied as a diluted solution in EtOH and sequential addition of substrate was used.