Square-wave cathodic adsorptive stripping voltammetry based on adsorptive accumulation is a very sensitive technique for the trace determination of xanthosine 5 0 -monophosphate (5 0 -XMP) and xantho-sine 5 0 -diphosphate (5 0 -XDP). The determination is based on the strong interaction of the adsorption of xanthosine phosphate compounds on a mercury elec-trode surface, forming Hg(II)-xanthate. The cathodic reduction of the accumulated Hg(II)-xanthate complex provides the basis for direct stripping measurements of the investigated biological compounds at sub-nanomolar concentration levels. Moreover, controlled adsorptive accumulation of the Cu(II) complex of xanthosine phosphate is also reported to assay trace amounts of xanthosine phosphate. The height of the sharp chelate peak of adsorbed Cu(II)-xanthate, coupled with the flat baseline, facilitates measurements at nanomolar and submicromolar concentration levels. The adsorption and the redox behaviour of the in-vestigated complexes are indicated by cyclic voltam-metry. Experimental and instrumental parameters for the quantitative determination were optimized. Statis-tical analysis of the calibration curve data is also included