Lysosomal proteinases, cathepsin B (CB) and cathepsin D (CD) have been implicated in the progression of several human tumors. In the present study, the antigen levels of CB and CD, and their immunohistochemical staining were compared in paired colorectal tumors (n =64) and background colon tissue of the same patients with clinicopathological staging. The antigen levels, were found to be significantly higher in cancer tissue (mean 35.79 ng/mg protein for CB and 3.97 ng/mg protein for CD) than in corresponding normal mucosa (24.62 ng/mg protein for CB and 2.69 ng/mg protein for CD). CB antigen levels were positively correlated with differentiation grade and Duke's stage (P < 0.001 and P = 0.041, respectively), but not correlated with nodal status. CD antigen levels were not correlated with the previous parameters. Staining intensity for both antigens increased from adenoma to adenocarcinoma. The degree of staining for CB and CD was associated with differentiation grade (P = 0.004 and 0.001, respectively), Dukes' stage (P = 0.002 and 0.001, respectively) and lymph node involvement (P = 0.002 and P < 0.001, respectively).