Two years later he passed his examination and in 1778 obtained the authorization to perform surgery in Valencia. Due to the siege of Gibraltar, he joined the corps of military surgeons as assistant second surgeon. By 8 April 1781 he had attained the rank of surgeon and joined the regiment at Zamora. As part of this regiment he went to America in the expedition of the Marquess of Socorro. From the Venezuelan port of La Guaira, he embarked for Havana, then for Veracruz, and was the director of the hospital of Xalapa for three months. In 1786 he was appointed surgeon-major of the military hospital of San Juan de Dios in Mexico City, then the capital of New Spain. After the merger of this hospital with that of San Andres in 1790, Balmis become director of venereal disease ward. In recognition of his work he was admitted to the (the predecessor to the Royal Academy of Medicine) and received his Bachelor of Arts from the University of Mexico.