Arylsulfatases A and B were measured in the stratum corneum of four normal controls and two individuals with sex-linked ichthyosis. For arylsulfatase A, the mean delta optical density/hr/mg protein value was 1.6 for controls and 2.0 for patients, whereas for arylsulfatase B values of 1.5 for controls and 1.4 for patients were observed. Assay of arylsulfatase C in the callus of four normal controls showed a mean delta optical density/hr/100 mg callus of 0.63, whereas no or trace activity was detected in callus from four patients with x-linked ichthyosis. The assay of steroid sulfatase is best for studying microsomal sulfatase activity. Table 1 shows the activity of this enzyme in nails, callus, and hair bulbs from controls and patients with x-linked ichthyosis. No steroid sulfatase could be demonstrated in patients with x-linked ichthyosis. The values in normal controls and obligate heterozygotes are compared in Table 2. The mean value of the two groups is statistically different with P less than or equal to 0.05 using the Student t test.