A mass spectrometric investigation has been carried out on dihydroxy- and tetrahydroxychlorins, derivatives of vic-dols of etioporphyrin-1 and octaethylporphyrin, the vic-diol and vic, vic-tetraol of the tetraethyl ester of coproporphyrin-1, dmers of bischlonns linked together with a methylene bridge, and also of their trimethylsitylated products. It was established that in the spectra of porphynn dots the molecular ion peaks were either of low intensity or were completely absent. In the spectra of trimethylsilyl derivatives, the ion peaks of maximum intensity were caused by the sitylation of only one of each two neighboring hydroxyl groups in the initial compounds.