Upon hearing a recording of Ferrer reciting these poems, accompanied by the guitarist Agustín Carlevaro, Piazzolla invited him to collaborate on the writing of the opereta María de Buenos Aires.

The work was premiered in 1968 in the Sala Planeta in Buenos Aires with Piazzolla and a ten-piece orchestra, the singers Héctor de Rosas and Amelita Baltar and with Ferrer as reciter in the role of El Duende.

Piazzolla and Ferrer now started to compose a series of tangos, with a clear social commitment, such as the well-known Chiquilín de Bachín and Juanito Laguna ayuda a su madre.

Other songs written by the Piazzolla-Ferrer duo at this time were Canción de las venusinas, La bicicleta blanca and Fábula para Gardel, included in the album Astor Piazzolla y Horacio Ferrer en persona.

He worked with a series of renowned tango musicians such as Roberto Grela, Leopoldo Federico and Paul Garello and with Horacio Salgán he composed the Oratorio Carlos Gardel in 1975.

The following year he wrote lyrics to Loquito Mio with Julio De Caro, Esquinero with Pedro Laurenz, El Hombre que fue ciudad with Armando Pontier, Yo payador me confieso with Osvaldo Pugliese and Tu penultimo tango with Anibal Troilo.