Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; The aim of this study was to investigate some of the factors affecting pectin lyase (PL) production by an Aspergillus giganteus strain, and to characterize this pectinolytic activity excreted into the medium. The highest activities were obtained with orange waste, citrus pectin and galacturonic acid as carbon sources. The highest activity, using citrus pectin as carbon source, was obtained in 11-day-old standing cultures, but the highest specific activity was obtained in 6.5-day-old shaken cultures, at pH 6.5 and 35A degrees C. Using orange waste as carbon source, the highest activity was observed in 8-day-old standing cultures, at pH 7.0 and 30A degrees C. Optimal assay conditions were pH 8.5-9.0 and 50A degrees C. The PL activity showed thermal stability, with half-lives of 30 and 27 min when incubated at 45 and 50A degrees C, respectively. High stability was observed at room temperature from pH 6.0 to 10.0; more than 85% of enzyme activity was preserved in this pH range. Under optimum conditions, the highest pectin lyase activity in the medium was 470 U/ml, with orange waste as carbon source.