Contamination of seedlings with a formulation containing an entomopathogenic virus at the time of transplanting was found to be a technically feasible method of introducing an insect virus into an agroecosystem. Cabbage so treated with the highly infectious, single-embedded nucleopolyhedrosis virus of the cabbage looper,Trichoplusia ni(Hübner), maintained a high concentration of the virus thoughout the season. In bioassays, larval mortality on treated plants averaged 97.2% during the 1st-week posttreatment and 95.0% throughout the 84 days of sampling. Larval mortality on untreated plants averaged 4.5% during the 1st-week posttreatment and increased to 89% by 84-day posttreatment due to spread of virus from treated plots.