A high-performance liquid chromatography (HPLC) method for creatinine has been developed. The method is based on ion-pair chromatography. The method is precise and easy to perform. Recoveries from enriched sera were from 98-105% with a mean of 100.5%. At 28 mumol l-1, 52 mumol l-1 and 487 mumol l-1 within-series standard deviations of 2 mumol l-1, 2 mumol l-1 and 10 mumol l-1, respectively were obtained. At 102 mumol l-1 among-series standard deviation of 6 mumol l-1 was obtained. Comparisons between HPLC and autoanalyser (Jaffé reaction) methods showed that the autoanalyser plasma and serum results, which are known to be sensitive to 'pseudocreatinines', varied between 93-217% of the HPLC results. Comparisons between HPLC, autoanalyser and enzymatic methods showed that the methods agree well for urine samples. The method presented appears suitable as a secondary reference method.