Efficiency in cotton bollworm Helicoverpa armigera Hübner controlusing neem seed powder and nuclear polyhedrosis virusInsect pest biological control potentially decreases the use ofchemical insecticides. The alternative control method chosen wascombination of botanical and microbial agents that showed highereffectiveness against H. armigera. This control method might alsopotential to minimize the use of chemical pesticide on cotton. Study onefficiency of cotton bollworm Helicoverpa armigera Hübner control usingneem seed powder (NSP) and nuclear polyhedrosis virus was conducted atAsembagus Experimental Station of Indonesian Tobacco and Fiber CropsResearch Institute, Situbondo, East Java, from January to December 2003.The objective of this study was to find out the efficiency level of cottonbollworm control using combination of neem seed powder (NSP) andnuclear polyhedrosis virus (NPV). The treatments were : (1) NSP(LC 25 ) +NPV(LC 50 ), (2) NSP(LC 50 ) + NPV(LC 50 ), (3) NSP (recommended dose),(4) NPV (recommended dose), (5) betacyfluthrin (recommended dose),and (6) control (untreated). The treatments were arranged in a randomizedblock design with three replications. Parameters observed were populationof H. armigera larvae and its complex predators, frequency of spraying,square and boll damage, cost of control, net income, marginal rate ofreturn, and yield of seed cotton and mungbean. The research resultsshowed that the combination of NSP(LC 50 )+NPV(LC 50 ) effectivelyreduced the total cost of insect control by 63.4% and increased the increase32.7% compared to betacyfluthrin. The combination also showed thehighest marginal rate of return of 4.66 and 4.28 based on control andbetacyfluthrin, respectively.