The yeast strain Kluyveromyces marxianus CDBB-L-278 is an outstanding producer of endopolygalacturonase (EC. 3.2.1.15); it has been reported that its production is repressed under high dissolved oxygen tension. The expression of the endopolygalacturonase gene (EPG) from this yeast was compared under both aerobic and anaerobic conditions and was related to the enzyme activity. Specific enzyme production under anaerobic conditions (0.233 uPG mg-1) was five times higher than that obtained under aerobic conditions (0.048 uPG mg-1), demonstrating that anaerobic growth promotes the synthesis of endo-PG; relative quantification of EPG gene expression was 21.19 times higher in anaerobic culture, suggesting that production of endo-PG under anaerobic culture conditions is a consequence of the regulation of the EPG gene by dissolved oxygen saturation in the growth medium. Results point out that the higher production of endo-PG under anaerobic culture conditions is a consequence of the regulation of EPG gene.