Deposition of glycosaminoglycans and laminin-1 in the renal corpuscles of the kidneys of mylencephalic blebs, 'blebs', (my) and normal C57BL/ 6J mice was compared in embryonic, neonatal (newborn to approximately two days old) and adult animals. Utilization of Alcian Blue 8GX staining, at a pH of 2.5, revealed an increase in acidic glycosaminoglycans in the parietal layer of Bowman's capsule and in general, an increase in the mesangial matrix of the glomerulus of my mutant adults. An increase in glycosaminoglycans was also noted in the developing kidney in certain my embryos in tissues associated with the glomeruli, but no significant differences were observed between the kidneys of neonatal my and control mice. The laminin-1 procedure revealed more deposition of laminin in the basement membrane of the parietal layer of Bowman's capsule in the neonatal and adult mutant my mice. Altered deposition of basement membrane and extracellular matrix components may reflect changes in the pattern of development and in the functioning of the kidney. Morphological changes in the human kidney are associated with alteration of function; a similar association may be occurring in the mice homozygous for the my gene.