The value of cathepsin B activity in determining the extent of disease was investigated in 106 patients with carcinoma of the cervix uteri and in 20 women with dysplasia of the cervix uteri. The measurements of serum and tumor cathepsin B activity were performed before treatment. The levels of cathepsin B were estimated by direct fluorimetric assay based on the use of 2-Phe-Arg-NMec as a substrate. The results show that the mean serum and tumor activity of this enzyme increase with progression of neoplastic disease and was closely dependent on clinical stage of cervical carcinoma. Also, we found higher serum and tumor levels of cathepsin B activities in patients with clinical early disease (FIGO Stage Ib and IIa) in whom metastases to pelvic lymph nodes were detected than in patients with disease limited to the cervix uteri (p < 0.001, t-test). Enhanced activity of cathepsin B was observed in 64% of patients with cervical carcinoma.