A high-performance liquid chromatographic method was developed for the determination of a new carbapenem, DA-1131 (I), in human plasma and urine and in rat blood and tissue homogenates. The method involved deproteinization of the biological samples with 1 volume each of 0.04 M Ba(OH)2 and ZnSO4 aqueous solution. A 50-microliters aliquot of the supernatant was injected onto a C18 reversed-phase column. The mobile phase employed was 0.015 M KH2PO4-acetonitrile (9:1, v/v) with a pH of 5.0. The flow-rate was 0.8 ml/min. The column effluent was monitored by a ultraviolet detector at 300 nm. The retention time of I was 8.0 min. The detection limits of I in human plasma and urine were 0.1 and 0.5 micrograms/ml, respectively. The coefficients of variation of the assay were generally low (below 8.39%) for human plasma and urine, and rat blood and tissue homogenates. No interferences from endogenous substances were observed.