This paper aims at analysing the autographic manuscripts of two plays written in collaboration, El mejor amigo, el muerto and La más hidalga hermosura. According to the title pages of their manuscripts and to their printed texts, Francisco de Rojas Zorrilla took part in the composition of the two comedies. In the sections of the texts that are ascribed to the Toledan dramatist several handwritings appear but none of them belongs to Rojas, according to the results of the comparison with autographic manuscripts signed by the author. Therefore, paleographical evidences states that Rojas is not to be considered one of the authors of the two plays.