Success has been achieved in detailed understanding of tautomeric and isomeric equilibria and search for the new tautomeric and isomeric forms of oximes of pyridoxal, pyridoxal-5'-phosphate and some of their analogs, their presence is explained. This is due to a careful deconvolution of absorption spectra of different ionic forms of oximes into bands corresponding to separate electronic transitions. The spectroscopical data and the results of quantum-chemical calculations are compared for all the forms of compounds under investigation. As it has been found to be valid for other vitamin B6 derivatives as well, quantum-chemical calculations can be used for analytical purposes.