Early detection and reliable monitoring of treatment constitute one of the most challenging problems in oncology. For this reason, we studied the potential value of serum cathepsin B-like activity as a possible marker of laryngeal carcinoma. The results indicate that serial analyses of this parameter have predictive value in the assessment of surgical treatment of laryngeal carcinoma. Activity of the enzyme reveals a progressive increment which could be associated with increased severity of the neoplasm present. The serum level of the cathepsin B-like activity remained close to zero in the control group of healthy volunteers and patients with inflammatory diseases.