Several neuromuscular disorders are associated with reductions in intramuscular adenosine triphosphate (ATP) and/or phosphocreatine (PCr). These alterations have been primarily characterized using ³¹P–magnetic resonance spectroscopy (³¹P‐MRS). We prospectively measured total creatine, PCr, and ATP in muscle biopsies from 81 patients: normal controls (n = 33), mitochondrial cytopathy (n = 8), neuropathic (n = 3), dystrophy/congenital myopathies (n = 7), inflammatory myopathy (n = 12), and miscellaneous myopathies (n = 18) using direct biochemical analysis. Intramuscular concentrations of PCr and ATP were lower for the dystrophy/congenital myopathy, inflammatory myopathy, and mitochondrial disease patients with ragged red fiber (RRF) as compared with normal controls (P < 0.05). Total creatine was lower for the dystrophy/congenital myopathy group as compared with the normal control group (P < 0.05). These values compare favorably to results from other studies using ³¹P‐MRS and provide external validation for the values obtained using that method. Given the reductions in high‐energy phosphate compounds in these patients, there is the potential for therapeutic intervention with creatine monohydrate supplementation. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 1228–1233, 1999.