We describe a rapid method for determining cholesterol sulfate in plasma and erythrocytes. After its single-step isolation by means of anion-exchange chromatography cholesterol sulfate is hydrolyzed, trimethylsilylated, and determined by gas chromatography with flame ionization detection. 5 beta-Cholestan-3 alpha-ol sulfate is used as internal standard. The method enables simultaneous determination of dehydroepiandrosterone sulfate in plasma. We applied it for the diagnosis of seven patients with recessive X-linked ichthyosis. Concentrations are given for plasma and erythrocytes from four unaffected relatives of patients with X-linked ichthyosis, a patient with placental sulfatase deficiency, two patients with other types of ichthyoses, and 20 controls. The method may also be of use for the rapid isolation of other organic sulfates from biological material, as illustrated by a comparison of gas chromatograms of urine from a normal pregnant woman and that from a patient with placental sulfatase deficiency.