A high-performance liquid chromatographic method was developed for the quantification of free malonaldehyde (MA) in tissues. HPLC separation was performed using a TSK G1000 PW column (7.5-mm i.d. X 30 cm) with a mobile phase of 0.1 M Na3PO4 buffer, pH 8.0, at a flow rate of 0.6 ml/min. The eluant was monitored at 267 nm. Free MA in the tissue sample was separated and quantified in approximately 50 min. The lowest amount of MA that can be determined by this HPLC technique is approximately 1 ng per injection. This method was successfully applied to rat liver and beef, pork, and chicken muscle and was compared to the thiobarbituric acid (TBA) test. It was found to be more sensitive, accurate, and specific for the determination of free MA than the TBA method.