A multiple-embedded nuclear polyhedrosis virus (MNPV) was isolated and characterized from a field-collected, fourth-instar yellowstriped armyworm,Spodoptera ornithogalliGuenée, in Boone County, Missouri. The LC50value of this virus was determined to be 0.42 occlusion bodies (OB)/mm2for first instar and 7.0 OB/mm2for third instar.Heliothis zea(Boddie),S. frugiperda(J. E. Smith), andPlutella xylostella(L.) larvae were not susceptible to this MNPV. Mortality was observed inTrichoplusia ni(Hübner) larvae challenged with high concentrations; however, no occlusion bodies were observed in or recovered from tissue of survivors or cadavers, and liquefaction of cadavers did not occur. This MNPV appears to be specific forS. ornithogalli; further studies against otherSpodopteraspecies may be justified.