High resolution proton nuclear magnetic resonance (NMR) spectra of normal and diseased human muscle extracts were recorded at 470 MHz. Resonances from lactic acid, creatine, glucose, ribose, purine and pyrimidine bases were identified. The longitudinal relaxation times of these resonances were determined to allow quantitation of muscle metabolites. With aid of a standardized reference capillary, inserted into the NMR tube containing the muscle extracts, the lactic acid and total creatine content of the extracts was determined. After 5 h of incubation at 37 degrees C, normal muscles contained on average 103 mumol lactic acid and 36 mumol creatine/173 mg of noncollagenous protein, equivalent to 1.0 g of fresh muscle. The lactic acid and creatine contents decreased slightly in scoliosis and idiopathic scoliosis and they decreased significantly in cerebral palsy. In an extract of a patient whose illness was diagnosed as 'scoliosis' no creatine was present, and in an extract of a patient with unknown diagnosis the creatine content was reduced to 2 mumol/173 mg of noncollagenous protein. The short time (1.7 sec to 6.5 min) and the small amount of tissue (300 mg) needed for an analysis add to the potential of proton NMR as a new technique for the characterization of muscular diseases.