This document summarizes an experiment investigating the resistance of cardenolide-sequestering insects to the toxic cardenolides produced by milkweed plants. The experiment involves measuring the activity of the Na+/K+-ATPase enzyme in the heads of red milkweed beetles and swamp milkweed beetles under varying concentrations of the cardenolide ouabain. While initial results using fruit flies as a control were successful, the results for the beetles were inconsistent and did not allow the hypothesis that swamp milkweed beetles have greater resistance to be accepted or rejected. Future work is needed improving the protocol and analyzing pure neurons to better understand the cardenolide resistance of these beetles.