In this article, a HPLC method to identify and quantify the dyes and the indigo precursors produced in Polygonum tinctorium is described. Using this technique, indican has been positively identified in extracts of P. tinctorium. Our work with two cultivars of P. tinctorium has confirmed that the quantity of indican is dependent on the cultivars, harvest period, and age of the leaves. Two enzymes, Novozym 188 (cellobiase) and Novarom G (beta-glucosidase), are compared on the basis of their activities to hydrolyze the indican at several pH values. We observed that Novarom G is more active than Novozym. 188 whatever the pH and that optimum pH of both enzymes for indican hydrolysis is 3. Liberated indoxyl can be oxidized in alkaline media and transformed into indigo and indirubin.