Iodometric Back Titration (TBT) and Spectrophotometric (SPM) methods are two common methods used in the determination of hydrogen sulfide concentrations in anoxic basins, like in the upper sections of the Black Sea anoxic waters. Although the results obtained by both methods are in agreement when the concentrations of sulfide are higher than 30 mu M/l, IBT analysis gives more reproducible results compared to SPM analysis. On the other hand, the reproducibility of the SPM is better than that of IBT method when the concentration of sulfides is less than 30 mu M/l, but in this case SPM method provides lower results compared to IBT method. This discrepancy can be explained by the presence of the hydrogen sulfide oxidation products (i.e., thiosulfate) formed as a result of aeration of water samples. These products consume the iodine added to the sample. Therefore, they are measured as hydrogen sulfide in the IBT method, but are not detected by the SPM method since they do not react with the N,N-dimethyl-p-phenylendiamine - FeCl3 mixed reagent.