The 7-benzylidenenaltrexone (BNTX) derivatives 2a–v, 3a–c, 13a–c, and 14a were synthesized from naltrexone (1) and evaluated for their antitrichomonal activity. The structure-activity-relationship studies found that 4-iodo-BNTX (2g) showed the highest activity (IC50 = 10.5 µM) and the affinity for the opioid receptor was less important for antitrichomonal activity against Trichomonas vaginalis. The