Decalcification of echinoderm tissues for electron microscopy can be achieved after glutaraldehyde-osmium fixation by treatment with a 1:1 mixture of 2% ascorbic acid and 0.3 M NaCl for 12-24 hours. Electron photomicrographs of material decalcified by this procedure are superior to those from EDTA-treated tissue and show few of the deleteriour effects produced by EDTA.