I am going to assume you mean the Miracle of Lanciano.
As for the miracle, it is said that in Lanciano, Italy, around the year 700 AD, a Basilian hieromonk (a hieromonk means he was either a priest who had taken monastic vows or a monk who was ordained to the priesthood) was assigned to celebrate Mass. At this Mass, however, the monk had doubts about the Real Presence of Jesus in the Holy Eucharist; as the monk said the Words of Consecration ("This is my body, this is my blood"), the monk saw the bread change into human flesh and the wine change into human blood which coagulated into five globules, which is said to correspond with the Five Holy Wounds that Jesus received on the Cross.
This event has been investigated six times since 1574; it was first examined by Bishop Antonio Gaspar Rodriguez in 1574, by Father Serafino in 1636, by Bishop Gervasone in 1777, by Bishop Petrarca in 1886, by Odoardo Linoli in 1971, and by the World Health Organization in 1973. According to Linoli's examination, the flesh is human flesh and the blood is human blood, the flesh is composed of muscular tissue from the heart, and both the flesh and blood contain the same blood type (AB).
Basilian monks kept the flesh and blood until 1175, when they were succeeded by Benedictine monks a year later, where the flesh and blood were placed in different locations in the Church of St. Francis in Lanciano. From 1636 to 1902, the flesh and blood were kept in Valsecca Chapel, until they were moved to a new altar where they may be seen today.
According to Wikipedia (and from other sources), this event is officially recognized by the Catholic Church and is authenticated as a Eucharistic miracle.