A method was developed for the comprehensive cartography of the selenium metabolites synthesized in the process of conversion of selenite [Se(iv)] into organic compounds and enrichment of yeast with selenium. The number of compounds detected was considerably increased (49) owing to the optimization of the fractionation procedure and the use of UPLC. The increased purity of the minor selenoorganic amino acids and oligopeptides allowed successful on-line de-novo identification based on the exact mass (<1 ppm) and fragmentation (MS(2)/MS(3)) mass spectra obtained with high resolution and high mass accuracy. The quality of mass spectra allowed the re-interpretation of previously reported structures of some selenium species.