The dependence of 1-naphthol sulfation on inorganic sulfate levels has been studied in isolated hepatocytes. Rates of sulfation of 1-naphthol (190 micron) depend on extracellular sulfate in a non-linear relationship, i.e. the dependence is more expressed at sulfate levels of the medium below 200 micron than at higher concentrations of the inorganic anion. Similarly, the intracellular steady state concentrations of 35SO2-(4) are a non-linear function of the extracellular sulfate levels, i.e. at low concentrations of extracellular sulfate the intracellular levels exceed those of the medium, while above 500 micron the ratio of the intracellular versus extracellular concentrations is lower than 1. The apparent Km value for intracellular sulfate in the overall sulfation of 1-naphthol amounts to about 500 micron. 4-Nitrophenyl sulfate markedly stimulates the formation of 1-naphthyl sulfate in intact cells as well as in cells permeabilized by freezing/thawing.