1. Glyceraldehyde 3-phosphate dehydrogenase [GPD, EC 1. 2.1.12] from vegetative cells of Bacillus cereus was purified and its molecular and catalytic properties were examined. The purified enzyme was homogeneous as judged by disc gel electro-phoresis with and without SDS and by electrophoresis on cellulose acetate strips at various pH values. The enzyme was a tetramer and the subunit molecular weight was 36, 000 which is exactly the same as that found for GPD from other sources.2. Analysis of SH groups with 5, 5'-dithio-bis(2-nitrobenzoic acid) showed that, in contrast to the enzyme isolated from muscle, there are only 8 SH groups per tetramer (MW 144, 000) of which 4 are highly reactive and essential for activity.3. CD spectra showed that the enzyme has a very high content of β-structure (45%) which seems to be common to other GPDs.4. The enzyme was fairly heat stable and was similar to Bacillus stearothermophilus GPD in many of its properties.