A sensitive and reproducible method for the determination of adenine nucleotides (ATP, IMP) and creatine compounds [creatine (Cr), phosphocreatine (PCr)] in freeze-dried single human muscle fibre fragments is presented. The method uses isocratic reversed-phase high-performance liquid chromatography of methanol extracts. Average retention times (min) of ATP, IMP and PCr, Cr from standard solutions were 10.6+/-0.42, 2.11+/-0.06 (n=6) and 10.5+/-0.31 and 1.19+/-0.02 (n=9), respectively. Detection limits in extracts from muscle fibre fragments were 2.0, 1.0, 3.0 and 2.0 mmol/kg dm, respectively. The assay was found successful for analysis of fibre-fragments weighing > or = 1 microg.