The field efficacy of the nuclear polyhedrosis virus of the armyworm, Mythimna separata (Walker) on sorghum was tested for two seasons (1991 and 1992) indicated that the NPV applied @ 500 LE/ha, registered 63.30, 72.79 and 76.31 per cent, while the standard insecticide endosulfan 35 EC recorded 76.08, 90.26 and 96.43 per cent larval mortality after 4th, 5th and 6th day of application, respectively. Though the virus alone at 500 LE/ha also could reduce the larval population significantly, there was an increase in viral dosage from 25 LE to 500 LE/ha. Hence the NPV @ 500 LE/ha was found to check the pest appreciably and was comparable with endosulfan insecticide treatment as there was no significant difference between these treatments.