Pulsed field gradient (PFG) spin echo 31P NMR can be used to measure diffusion coefficients of phosphorus-containing metabolites in vivo. In biological spin echo spectra, the ATP resonances are phase modulated by J-coupling between the three phosphorus atoms. This phase modulation may severely decrease the apparent signal intensity of the ATP peaks. In this paper, we describe the use of homonuclear decoupling during spin evolution to suppress the effects of J-coupling in biological spin echo spectra. Phosphorous spectra of ATP and creatine phosphate (PCr) in solution and goldfish (Carassius auratus) skeletal muscle demonstrate the effectiveness of homonuclear decoupling in improving the effective signal-to-noise ratio of ATP. In addition, diffusion coefficients of ATP and PCr determined in goldfish skeletal muscle show that PFG homonuclear decoupled spin echo (HDSE) NMR provides accurate measures of diffusion coefficients.