Iodometric Back Titration (IBT) and Spectrophotometric (SPM) determination are two commonly used methods for the determination of hydrogen sulfide (H2S) concentration in sea water. These two methods were applied in parallel for analysis of Black Sea anoxic waters and artificial solutions containing different H2S concentrations. The results of the SPM and IBT methods are in agreement when the HIS concentration in sea water is higher than 30 mu M and the precision of IBT is higher than that of SPM method. However, an opposite trend appears when the concentration of sulfide is less than 30 mu M; moreover, the SPM method provided lower results than the IBT values. This apparent difference is most probably due to the presence of some hydrogen sulfide oxidation products (e.g., thiosulfate) consuming the iodine solution added to samples, but the complexing agent (N,N-dimethyl-p-phenylendiamine) used in SPM method, reacts with H2S only.