Intratesticular injection of EsterilSol (zinc gluconate neutralized with arginine) is a chemical sterilant for male dogs sometimes used in population control campaigns. Adverse reactions have been reported in 1% to 4% of treated dogs, but detailed histomorphologic descriptions are lacking. During a behavioral study conducted in the Chilean Patagonia in 2012, severe necrosuppurative orchitis and ulcerative dermatitis were observed in 2 of 36 (6%) dogs sterilized with EsterilSol according to the manufacturer's instructions. Reactions were noted on days 8 and 7 postinjection and required scrotal ablation on days 8 and 13, respectively; neither reaction was associated with the injection site. Although self-trauma following administration may have contributed, the cause of the adverse reactions is uncertain. EsterilSol is a relatively uncomplicated method to sterilize male dogs, but the occurrence of severe adverse reactions several days after administration emphasizes the need for the provision of long-term monitoring and veterinary care during sterilization campaigns using this product.