This technology includes a group of at least twenty-nine, diverse, commercially available compounds that are newly identified for activity against Giardia lamblia parasites. At least six of the candidate compounds, Bortezomib, Decitabine, Hydroxocobalamin, Amlexanox, Idarubicin, and Auranofin have preexisting FDA approval for human use for other (non-Giardia) conditions. Another three compounds, Fumagillin, Nitarsone and Carbadox have preexisting approval for veterinary use for non-Giardia conditions. Additional active compounds identified include: Acivicin, Riboflavin butyrate, BTO-1, GW9662, Dinitroph-dfgp, Deserpidine, Tetramethylthiuram disulsulfide, Disulfiram, Mitoxantrone, Ecteinascidin 743, 17-allyaminogeldanamycin, Carboquone and Nocodazole. The anti-Giardial activity of these compounds presents a cost saving opportunity for the rapid development of new, better tolerated treatments for the most prevalent human intestinal parasite infection in the United States and the world.