Fr. Uguccione, parish priest at Sant'Ambrogio in Florence, celebrated Mass on December 30, 1230. After the Mass, in his haste, he failed to fully purify the chalice — a small amount of consecrated wine remained. The next morning, when the chalice was opened, the wine had visibly transformed into a clot of fresh, bright red blood adhering to the inside of the cup.
The bishop investigated; the relic was preserved. A second Eucharistic phenomenon occurred at the same church in 1595, when the tabernacle survived a fire that destroyed the surrounding structure and the consecrated hosts were found untouched. Both relics are venerated at the Church of Sant'Ambrogio.