A coupled enzymatic assay was developed for quantitative determination of the stereoisomeric products formed in aldol reactions catalyzed by dihydroxyacetone phosphate (DHAP)-dependent aldolases. Three of the four stereoisomers could be determined directly; the fourth one was calculated. This procedure is based on the reversibility of the aldol reaction and requires no derivatization or work-up of the product samples, only removal or inactivation of the biocatalyst. In comparison with other methods the enzymatic assay is highly accurate and fast. Determination of isomer formation with 10 different acceptor substrates applying this procedure gave unprecedented insight in the stereochemistry of fructose-1,6-bisphosphate aldolase from Staphylococcus carnosus and L-rhamnulose-1-phosphate aldolase from E, coli.