The subject is taken from the apocryphal Book of Tobit. Tobias was sent by his blind father, the merchant Tobit, to collect a debt. 'Ricordo' (memorandum) is written on a small scroll in the boy's hand. The Archangel Raphael who accompanies Tobias instructs him to extract the heart, liver and gall from a fish as a cure to heal his father's blindness. Raphael is shown holding a small box containing the remedy.
The story of Tobias and the angel was a popular subject in late 15th-century Florence, where a confraternity of Saint Raphael flourished. Raphael was venerated as a protector of travellers and as a healer. The theme of filial piety, enterprise and charity was important for the merchant families of the city.
It is likely that more than one artist worked on the painting, consistent with practice in Verrocchio's workshop. Some areas, for example the landscape, are rather weak. On the other hand, the more accomplished parts - most notably the dog and the fish - have been proposed as the work of the young Leonardo, though they may have been added by Verrocchio himself.