Abstract: In a method for the quantative enzymatic determination of adenosine diphosphate (ADP) in aqueous solution by phosphorylation of the ADP with a kinase in the presence of a phosphorylated substrate therefor, with the formation of ATP and a dephosphorylated substrate, such as galactose, formate, pyruvate or nucleoside diphosphate, the dephosphorylated substrate is reacted, optionally with the insertion of a further adjuvant reaction, such as a decarboxylation, transamination or hexosidiation, with NAD(P) in the presence of a dehydrogenase and the NAD(P)H formed is either measured directly or reacted with a tetrazolium salt in the presence of an electron carrier, with the formation of a formazane, which latter is then measured.