Reverse transcription polymerase chain reaction (RT-PCR) was applied in the detection of herpes simplex virus-1 (HSV-1) mRNA from tear film and corneal epithelium in a murine herpetic keratitis model. The diagnostic value of this new technique for acute herpetic keratitis was evaluated in comparison with direct PCR for genomic DNA and viral culture. On day 2 postinfection (PI) of HSV, all mice showed dendritic keratitis, and PCR, RT-PCR, and viral culture were positive in all samples. On day 8 PI, no dendritic keratitis was observed in any mouse, PCR was positive in all samples, while RT-PCR was positive in only 5 of 12 samples and viral culture in only 2 of 12. The sensitivity of RT-PCR was lower than that of PCR, and approximately the same as viral culture; however, the findings of RT-PCR more closely concurred with clinical observations than the findings of PCR. These results show the potential of RT-PCR for rapid, specific diagnosis of acute herpetic keratitis.