Since the demonstration that acid mucopolysaccharides accumulate in tissue and urines of patients with the Hurler and Hunter syndromes, other mucopolysaccharidoses have been described. Some lipid storage diseases have also been shown to have an increase in acid mucopolysaccharide with the lipid material stored. Tissue culture technics have shed some light on several aspects of these diseases especially with regard to genetic counselling. Available information is reviewed in an attempt to reconcile current knowledge in arriving at a unifying hypothesis. © 1969.