1. The sucrose, raffinose and inulin spaces within the gastrocnemius of the female rat have been estimated at 12.0 +/- 2.2%, 10.7 +/- 0.6%, and 10.0 +/- 0.3% respectively, expressed as a percentage of the total muscle volume.2. The mucopolysaccharide and hexosamine contents of the gastrocnemius have been found to be inversely dependent upon the weight of the muscle.3. The possibility that a relation exists between the saccharide spaces and the muscle musopolysaccharide content has been discussed in terms of saccharide molecular radii.