A recombinant strain of Aspergillus awamori expressing anti-lysozyme single chain antibody fragments (scFv), under the control of a xylanase promoter, was studied in order to investigate the impact of medium, induction regime and protease production on the expression of the product. Experiments with the time of induction showed that the optimum results are achieved when induction is started in the late exponential phase (21 h after inoculation) improving the titer of the product from 14.5 mg L-1, obtained in the early exponential phase (7 h after inoculation), to 16.2 mg L-1. A 100% increase of the carbon (fructose) and nitrogen (ammonium sulfate) sources in the growth medium resulted in an increase in product concentration from 16.2 to 108.9 mg L-1 and an increase in maximum dry cell weight from 7.5 to 11.5 g L-1. A 50% reduction in the concentration of the inducer resulted in an increase in the product yield from 10 ing g(-1) dry cell weight to 12 mg g(-1). Proteolytic enzymes were produced during the fermentation up to concentrations equivalent to 1.4 g L-1 trypsin, but they had no detrimental effect on the concentration of the antibody fragment.