Penicillium griseoroseum was grown in a 20 1 fermenter under different degrees of mixing and aeration to evaluate the effect of these variables on fungal macroscopic morphology and growth, as well as on production of pectin lyase (PL). A 2(4-1) fractional factorial design was used. Growth time was divided into two periods: the initial phase, comprised the first 25 h and the final phase, 25 to 60-72 h of growth. Pellet formation was the predominant growth form and no morphological differences were observed between treatments. Increasing the initial mixing rate from 50 to 200 rpm favored increased PL activity (U/g), but increasing the final mixing rate from 200 to 300 rpm did not influence it significantly. Combined analyses of the initial and final aeration rates showed that only the combination of no initial aeration and a final aeration rate of 20 l/min reduced PL activity (U/g). (C) 2002 Elsevier Science Ltd. All rights reserved.