The present study investigates the ability of several hexachlorobenzene (HCB) metabolites to induce porphyrin accumulation in chick embryo liver cells in ovo, in order to further clarify the role of metabolites in the mechanism of HCB-induced porphyria. HCB per se had no effect on liver porphyrin content, but pretreatment assays with phenobarbital suggested that its metabolic products did. When the direct effect of phenolic, sulfur-containing, and benzenic metabolites of HCB were tested, the following results were obtained. Less chlorinated benzenes (pentachlorobenzene and 1,2,3,4- 1,2,3,5- 1,2,4,5- tetrachlorobenzene) had poor capacity to change the control porphyrin content. On the other hand, the behavior of phenolic metabolites (pentachlorophenol, 2,3,4,5- 2,3,4,6- 2,3,5,6- tetrachlorophenol, 2,3,4- 2,3,5- 2,3,6- 2,4,5- 2,4,6- 3,4,5- trichlorophenol and tetrachlorohydroquinone) as porphyrin inducers was remarkable; the stronger effects were produced by trichlorophenols and tetrachlorohydroquinone. Sulfur containing metabolites produced increases in porphyrin content that were lower than those produced by phenolic compounds and higher than those due to the action of less chlorinated benzenes; only 1-methyl-(2,3,4,5-pentachlorophenyl) sulfoxide was not able to increase porphyrin level. The extent of the effect of the other drugs was pentachlorothiophenol greater than 1-methyl-(2,3,4,5,6-pentachlorophenyl) sulfone greater than tetrachlorothioanisol greater than pentachlorothioanisol. Regarding the mechanism of HCB porphyria, the present results indicate that phenolic metabolites and, in a lower degree, sulfur-containing metabolites, can contribute to the porphyrinogenic ability of HCB.