Transgenic varieties (Bt) are becoming more widespread in cotton plantations in Argentina, reaching about 10,000 hectares in the 1999/2000 campaign. In this paper, we carried out an economic analysis to find out differences between transgenic (Bt) and conventional varieties in terms of costs and income. We analyzed the information provided by 32 growers who are using this technology. To calculate Bt additional benefit per hectare, we used the partial budget method. Overall results show that Bt income surpassed $159.02 /ha and the additional benefit of using it was $65.05 /ha. Bt total direct costs, yield, and fiber quality were better. When using the Bt variety, the number of insecticide applications decreased 2.41 times (63.74 %) and costs by $27.55 /ha.