The Spodoptera littoralis nucleopolyhedrovirus (SlNPV) is a potential pest control agent of Spodoptera spp. As part of our studies to establish the use of this virus, a polymerase chain reaction (PCR)-based method was developed for the detection of viral DNA in infected insects. PCR amplification of the polyhedrin sequences enabled the detection of low levels of viral DNA directly from viral occlusion bodies or from total larval DNA. The use of different sets of synthetic DNA primers allowed us to differentiate between SlNPV and the Autographa californica NPV (AcNPV) and to identify a new AcNPV variant isolated from a cotton pest, Pectinophora gossypiella NPV. The PCR method was also used to test for the possible infection of Locusta migratoria larvae by SlNPV, reported by Bensimon et al., 1987. The progress of SlNPV infection in L. migratoria larvae was monitored by PCR for 2 weeks. The reaction revealed decreasing amounts of viral DNA in infected larvae. During this time, no signs of disease were observed in the infected locusts.