The glass transition (alpha) and secondary transition (beta) are compared in various aliphatic polyamides swollen by water, alcohol and acid. For all these polymer-solvent systems, the evolution of the temperature T alpha with the equilibrium sorption ratio presents two regimes. In the low-concentration regime, the dependence of T alpha on the number n of absorbed solvent molecules per accessible amide group follows a master curve independent of the nature of the system. No master curve is, however, observed for the beta transition. In the second regime, above a critical ratio n(*) dependent on the nature of both the solvent and the polymer, T alpha levels off, and the maximum concentration of absorbed solvent is proportional to n(*). These effects are explained in terms of solvent clustering around the amide groups.