The aim of this work is to present a concise analysis of the parliamentary immunity prerogative in relation to the right to equality. According to that established in a pre-constitutional Law of 1912, if the Legislative Chamber denies a rogatory letter, the criminal case is definitively rejected and it can not be reopen in the future, when the parliamentarian involved in the case leaves his or her position. We have made an analysis of the equality in the constitutional seat in order to verify if the aforementioned Law of 1912 is or is not contrary to the right to equality which is recognized in the article 14 of the Spanish Constitution. 334 MARIA ISABEL MARTIN DE LLANO