Bioconversion of wheat straw using Phanerochaete chrysosporium was carried out in a 200 1 staged vertical reactor. The bioconversion process was characterized by measuring the percentage degradation of lignin and cellulose, and increment in crude protein content. The effect of airflow rate, inoculum amount and wheat straw loading oil bioconversion was investigated using a statistical experimental design. An analysis of variance was performed to determine response surfaces. The quality of bioconversion indicated by an optimization index called the desirability coefficient had the highest value of 0.75 for the fifth day of cultivation. This corresponded to an operating condition of 1.5kg wheat straw per stage using an inoculum amount of 0.38g (100g dry wheat straw)(-1) and an airflow rate of 15 1 min(-1). The lignin and cellulose degradation achieved at this operating condition was 27% and 29%, respectively. A ratio of 3 for the weight of wheat straw to inoculum amount gave the highest crude protein of 5.9% oil dry weight basis. Among the variables investigated, the airflow rate exhibited a significant effect on the quality of bioconversion. Our results indicate that the quality of bioconversion may be controlled by implementing a predetermined airflow rate schedule. (C) 2008 Elsevier Ltd. All rights reserved.