It has been found that solutions of Zn-etioporphyrin in N-containing organic bases (lutidine, N-methylpiperidine, triethylamine), frozen at -196C, are capable of photochemical conversions. Comparison of the properties and spectral characteristics of the photoproducts formed with properties of protonated Zn-etioporphyrin dianions, produced by chemical methods, permits the following scheme to be proposed for conversion of Zn-etioporphyrin in organic bases (P, Zn-etioporphyrin molecule; D, molecule of base, which is both an electron donor and a proton donor to the P molecule). The first stage observable spectrally is photoreduction in the frozen solution. The hydroderivative formed in frozen solution is capable of again splitting off a proton during irradiation. Thermal addition of a proton to the PH(-) and its subsequent photocleavage in frozen solution can be reproduced repeatedly in one and the same sample. The central metal atom has a significant effect on the photochemical behavior of a methyl-porphyrin in solution.