Cotton (Gossypium hirsutum L.) genetically modified to express protein(s) derived from the soil bacterium Bacillus thuringiensis (Bt), and specifically toxic to caterpillar (Lepidoptera) pests, has been sold commercially since 1996.  On the continent of Africa, only South Africa has approved the commercial use of Bt cotton.  Recently, over three field seasons (2003?2005), second-generation Bt cotton (Bollgard II, Monsanto Co., St. Louis, MO) was tested in confined field trials in the west African country of Burkina Faso.  Observations of pest density, seed cotton yields, and the cost of insecticide sprays were evaluated in an economic model under a wide range of theoretical Bt technology cost premiums to determine the potential relative profitability of Bt cotton and conventional cotton.  Results averaged over three seasons indicate a Bollgard II yield advantage of 15% under conditions of low to moderate lepidopteran pest pressure, while insecticide sprays were reduced by two-thirds in the Bt cotton plots.  According to the economic model, Bollgard II remained profitable to the grower throughout the range of theoretical technology premiums evaluated ($0?75 per hectare) and was represented by economic gains of $79 to 154 per hectare.  Due mainly to the relatively low pest densities encountered at these research sites, the authors suggest that the model results presented may, in fact, underestimate the profitability of Bt cotton in Burkina Faso.