A simple procedure has been devised for the purification of alpha-glycerophosphate dehydrogenase (EC 1.1.1.8) FROM Drosophila melanogaster. The method involves substrate elution of the enzyme from a carboxymethyl cellulose column, followed by salt elution from agarose-hexane-AMP and DEAE columns. The procedure requires only 3 days to complete, results in high yield, and preparations that appear homogeneous by several criteria. A subunit molecular weight of 31 700 was obtained by sodium dodecyl sulphate electrophoresis in 10% acrylamide gels. This value is half that published for the native enzyme, confirming the homodimeric structure of this enzyme suggested by genetic evidence.