In answering the question as to what role possible metabolites of hexachlorobenzene play in the procreation of toxic hexachlorobenzene porphyria in rats, both pure hexachlorobenzene and different mixtures were fed to them. In each case 20% of the hexachlorobenzene was replaced by pentachlorophenol, 1,2,4,5-tetrachlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,3,5-tetrachlorobenzene, 2,3,4,5-tetrachlorophenol, 2,3,5,6-tetrachlorophenol, 2,3,4,6-tetrachlorophenol or chloranil. The determination of porphyrins at different intervals once the feeding had started did not give rise to an increase in the porphyria in any of these substances--which are seen as metabolites of hexachlorobenzene. Instead there was a distinct decrease in individual cases. From this the conclusion is drawn that none of the tested substances is the metabolite of hexachlorobenzene, which is in fact responsible for the hexachlorobenzene porphyria.