Sorption of bromocresole purple on the surfaces both of an unheated and heated biopolimer was studied at varying concns. of the active substance and acidities of solns. The sensitivity of the test was defined as the max. difference between the sorption capacities on both biopolymers. The highest sensitivity of the test was obsd. for the HCl concn. 0.5 mol/L and active substance concn. 0.16 mg/cm(3).