Growing evidence indicates that lysosomal Cathepsins D (CD), B (CB) and L (CL) may promote carcinogenesis and tumor progression. Therefore, we evaluated their potential value as biochemical parameters of malignant progression in patients with benign diseases which may undergo malignant transformation, such as liver cirrhosis (LC) and chronic pancreatitis (CHP) as well as in hepatocellular carcinoma (HCC) and pancreatic cancer (DPC). CD, CB and CL serum levels were determined by immunoenzymatic assays in LC, CHP, HCC or DPC patients and correlated with a number of biochemical and clinical parameters of these diseases. CD serum levels were increased in LC, CHP and HCC, but not in the DPC group as compared to normal subjects (NS) (P < 0.01). Interestingly, higher levels of this enzyme were observed in LC patients compared to HCC patients ( P < 0.01). CB serum concentrations were increased in all patient groups (P < 0.01). However no difference was evidenced between benign and malignant diseases. CL serum levels were significantly increased only in DPC as compared to NS (P < 0.01) or CHP patients (P < 0.02) and in HCC as compared to NS (P < 0.01). The evaluation of CD, CB and CL serum pattern in LC, CHP, HCC and DPC patients may be useful as additional biochemical parameters in the differential diagnosis and therapeutic monitoring of these diseases. Prospective clinical investigations to assess the potential value of these enzymes as biochemical markers of malignant progression of LC or CHP are warranted by the present data.