A quick and sensitive method for the determination of AMP, ADP, and ATP levels in mantle tissue of the sea musselMytilus galloprovincialis Lmk. is described. The method uses ion-pair high-performance liquid chromatography with diode array detection, allowing obtaining of the UV absorption spectrum for each peak. Method precision was good. The detection limit for all three nucleotides was 20 pmol (much lower than the minimum concentrations in this tissue).