A case of a child with Sanfilippo B syndrome (MPS III B), born of a consanguineous marriage, is reported. Urinary mucopolysaccharide analysis showed an abnormal excretion mainly of heparan sulphate. N-acetyl-a-glucosaminidase activity was absent in the patient but was present in the heterozygous range in parents and siblings. CSF mucopolysaccharides were also abnormally high. In fibrocytes from conjunctival biopsy and CSF cells numerous vacuoles containing storage material were found. The presence of vacuoles in fibrocytes from conjunctival biopsy and/or in CSF cells can be useful in the diagnosis of many suspected lysosomal storage disorders.