Technical Abstract: Although grandlure and boll weevil pheromone are comprised of the same four components, the ratio of the four components in grandlure and boll weevil pheromone differ considerably. Thus, the existing grandlure formulation may not be the most effective blend for attracting boll weevils to traps. We conducted a trapping study to compare the attraction of boll weevils to standard grandlure and an experimental formulation of grandlure which matches the component ratio of pheromone produced by boll weevils. Twenty-five to 80 pairs of traps were established at three locations in Mexico (Ojinaga, Durango, and Tamaulipas) and at two locations in South Texas (near Jourdanton and Weslaco). One trap in each pair was baited with standard grandlure and the other trap contained the experimental formulation. Traps were serviced weekly for four to eight weeks and the numbers of weevils captured in each trap were recorded. Statistical differences in the numbers of captured boll weevils were not detected between the two formulations at any of the evaluation sites. Thus, boll weevils appeared to be equally attracted to both formulations of grandlure. Considering the increased formulation cost of the experimental grandlure and lack of difference in the numbers of captured weevils, we found no justification for altering the existing commercial formulation of grandlure. In light of these findings, we suggest research efforts and eradication programs focus on other lure-related issues (e.g., pheromone dose, lure replacement interval, and lure dispenser technologies) to improve the performance of traps in detecting incipient boll weevil populations.