This paper presents a comparative, descriptive study on the social profiles and political trajectories of senators, federal deputies and their eventual substitutes who served in the National Congress from the 47th until the 54th Legislature. The objective of the study is to analyze, in each House of the Congress, the differences between senators and their eventual substitutes and between deputies and their eventual substitutes regarding (in relation to) their profiles and trajectories. The paper examine the hypothesis that the discretionary rule of indicating substitutes in the Senate results in a distance between senators and substitutes regarding their profiles: the elected senators are more experienced and qualified for the representation than their substitutes; in the Chamber, on the other hand, the substitution rules -which are the same way in which they are elected -are more democratic, there are fewer differences between elected representatives and their substitutes regarding (in relation to) their profiles. Analysis of the data on 942 profiles of senators and 4.961 profiles of deputies corroborate this hypothesis: senators are more experienced than their substitutes, while representatives at the Chamber and their substitutes have more similar profiles