1. Hexosamine estimations in the grey matter of 7 cases of Tay Sachs disease and of 7 cases of other forms of Amaurotic idiocy show that ganglioside accumulation is a

2. A glycolipid, Globosid I, with a terminal N-acetyl-D-galactosamine is found in both cell types; it reacts poorly, if at all, with an agglutinin anti-AHP from Helix pomatia, which, according to present knowledge, should react with this terminal hexosamine.