The present work describes the inducive effect of cresoquinone on microbiological transformation Of L-tyrosine to 3,4 dihydroxy phenyl L-alanine (L-DOPA) by Aspergillus oryzae NG-11(P1). Mould mycelium was used for biochemical conversion Of L-tyrosine to L-DOPA because tyrosinases, beta-carboxylases and tyrosine hydroxylases are intracellular enzymes. The maximum conversion Of L-tyrosine to L-DOPA (0.428 mg/ml) was achieved after 60 min of biochemical reaction. To enhance the production Of L-DOPA, cresoquinone was added to the reaction mixture. Best L-DOPA biosynthesis results were observed when the concentration of cresoquinone was 3.5 x 10(-6) M (1.686 mg/ml L-DOPA produced with 1.525 mg/ml consumption Of L-tyrosine). Cresoquinone not only increased enzyme activity but also enhanced cell membrane permeability to facilitate secretion of enzymes into the reaction broth. Comparison of kinetic parameters revealed the ability of the mutant to yield L-DOPA (Y-p/x [i.e., mg L-DOPA formed (mg cells formed)(-1)] =7.360 +/- 0.04). When the culture grown on various cresoquinone levels was monitored for Q(p), Q(s) and q(p) [Q(p): mg L-DOPA produced ml(-1) h(-1); Q(s): ing substrate consumed ml(-1) h(-1); qp: mg L-DOPA formed (mg cells)-' h(-1)], there was significant enhancement (P < 0.025) of these variables.