To improve the detection of lactate dehydrogenase-elevating virus (LDV), we developed a PCR assay. Primers were selected from ORF7, encoding nucleocapsid protein VP1. No specific amplification was observed with any other common murine virus or with RNAs from the closely related Lelystad virus and equine arteritis virus. In experimentally infected mice, LDV could be detected in plasma in both the acute and the persistent phases. LDV was also detected by the PCR in contaminated pools of Plasmodium berghei parasites which were maintained in mice, both by a direct analysis of the samples and by testing of plasma from mice inoculated with these pools. There was a complete agreement between the results of the PCR assay and the lactate dehydrogenase (LDH) enzyme assay of plasma from the inoculated mice. In contrast to the results of the LDH enzyme assay, no false-positive reactions were obtained in the PCR assay with negative control samples showing visible hemolysis. Storage of plasma samples at room temperature and at 4, -20, and -80 degrees C for up to 8 days did not influence the results of the PCR. These results show that the PCR is a valuable technique which may replace the LDH test as a diagnostic tool.