Publisher Summary This chapter describes an assay method and the purification procedure for fructose-bisphosphate aldolase from Ascaris suum . The assay is based on the oxidation of NADH by dihydroxyacetone phosphate (DHAP) in a coupled system containing triosephosphate isomerase and α-glycerophosphate dehydrogenase. The purification process involves extraction, ammonium sulfate precipitation, substrate elution from phosphocellulose column, diethylaminoethyl (DEAE)-Sephadex chromatography, and crystallization. Crystalline ascarid muscle aldolase is homogeneous by polyacrylamide gel electrophoresis and sodium dodecyl sulfate-gel electrophoresis reveals one protein band. The enzyme has a molecular weight of approximately 155,000–160,000 and is composed of four subunits of identical molecular weight. Ascarid aldolase exhibits a high degree of homology in amino acid composition to vertebrate muscle aldolase. Immunological studies indicate lack of common immunological determinants between rabbit aldolases A and B and ascarid aldolase. Free-living nematode Turbatrix aceti aldolase differs in amino acid composition from Ascaris suum to the same extent as it differs from that of aldolases from mammals.