At the end of 1582 Pietro Ponzio, maestro di cappella of Milan’s cathedral (Duomo), left his position: he would be replaced by Giulio Cesare Gabussi, a young musician found by archbishop Carlo Borromeo himself after an epistolary exchange with Costanzo Porta. During the period of researching, however, Ottaviano Abbiato de’ Forieri, a member of Capitolo, wrote to Borromeo suggesting as maestro di cappella Gian Giacomo Gastoldi and Luca Marenzio, two of the most important musicians of the late 16th century. This paper presents Ottaviano’s letter: an important document previously unknown.