Using histochemical methods, the presence of acidic glycosaminoglycans in the cell nuclei of 51 human irides and a series of monkey organs was demonstrated. In general, these substances are sensitive to testicular hyaluronidase and chondroitinase ABC and also to Streptomyces hyaluronidase, when using special staining methods. The specificity of testicular hyaluronidase was tested by. inhibition with heparin. By simultaneously staining with alcian blue and Feulgen, acidic glycosaminoglycans can be distinguished from the nucleic acids. Sporadically, hyaluronidase-resistant substances with a specific acidic glycosaminoglycan stainability occur. We assume the existence of various acidic glycosaminoglycans in the cell nuclei. Aging changes were not traceable with constancy.