We investigate experimentally one of the main features of a quantum fluid constituted by exciton polaritons in a semiconductor microcavity, that is quantum degeneracy of a macroscopic fraction of the particles. We show that resonant pumping allows to create a macroscopic population of polaritons in one quantum state. Furthermore we demonstrate that parametric polariton scattering results in the transfer of a macroscopic population of polariton from one single quantum state into another one. Finally we briefly outline a simple method which provides direct evidence of the first-order spatial coherence of the transferred population.