This paper explains how and why interest groups get access to the parliamentarian arena. The units of analysis are the number of hearings and the number of interest organizations per hearing classified by issue, parliamentary committee and time, and the independent variables are  institutional factors –mainly the electoral cycle and the type of government—, agenda capacity –measured by the number of committees, its size and number of bills they have to deal with— and party preferences –measured by the level of concentration of seats per committee. Following existing research we expect the number of hearings to increase under minority governments,  in the second and third year of the legislature and as a result of increasing agenda capacity. By the same token we expect the number of interest organizations per hearing is inversely related to the level of concentration of seats by committee –the more the concentration the less the number and diversity of interest organizations—. To do this we depart from the databases created by the Spanish Policy Agendas Project www.ub.edu/spanishpolicyagendas about all the Comparencencias, parliamentarian committees and bills introduced from 1996 to 2011 in the Congresos de los Diputados. Results illustrate participation of interest organizations in the parliamentarian arena vary across time, and this is related not only to a functional logic oriented to fulfill MPs need of information regarding specific issues, but especially party preferences.