The concentration of total and protein-bound hydroxyproline in the serum and total hydroxyproline in the urine was measured in the group of 52 patients with larynx carcinoma by means of Prockop's and Udenfriend's colorimetric method modified by Tomaszewski. The mean level of total and protein-bound serum hydroxyproline in the group of clinical patients was statistically significantly raised when compared with control group. The mean level of total hydroxyproline in the urine of patients with larynx carcinoma was statistically insignificantly raised when compared with control group. The degree of clinical or organic progress of larynx carcinoma was not found to influence essentially the level of hydroxyproline in the serum of the examined patients. It was shown however, that statistically essential increase in the total hydroxyproline level in the urine depends on the degree of organic progress of larynx carcinoma.