SummaryTwo children in a family with five siblings were investigated because of low levels of fibroblast arylsulfatase A activity. Neither child had metachromatic leukodystrophy (MLD) and they were diagnosed as having benign pseudo arylsulfatase A deficiency trait (PD). Analysis of arylsulfatase A subunit profiles in fibroblasts provided data for genotype assignments for each family member. Father and mother were assigned an n/pd and n/mld phenotype, respectively. The low enzyme siblings were both assigned pd/mld; two of the three normal enzyme siblings were assigned an n/n phenotype and one an n/mld.AbbreviationsMLD, metachromatic leukodystrophyPD, pseudo arylsulfatase A deficiencyN, normal