Reduction of murexide at the dropping mercury electrode was investigated. Data obtained at different concentrations in the range 0·5-2 mM showed that the half-wave potential of murexide was −0·38 voltvs. S.C.E. in 0·1 N KCl solution (neutral pH) and was not altered with concentration; with this last, the diffusion current increased linearly. Analysis of the plots log (i/id−i) vs. E indicated that the reduction was irreversible in nature.