Phosphorus NMR spectra were recorded for complexes of Na2ATP and Li4ATP with varying concentrations of magnesium, calcium and lithium. Each ion caused a shift in the phosphorus resonances, usually downfield, and a decrease in the 31P-31P coupling constant. The sodium ATP formed a 1:1 complex with each ion and a 1:2, ATP:Mg complex with magnesium whilst lithium ATP gave evidence to suggest the formation of bis(nucleotide) complexes.