Abstract.We discuss the validity of the rotating-wave approximation (RWA) focussing in particular on the micromaser dynamics. We consider the full Hamiltonian -given by H = ω0σz + ωa-for the description of the atom-field interaction. We arrive at the conclusion that the so called counter-rotating terms, (aσ − and a + σ + ) -which are neglected within the RWA -could give rise to physically observable effects for a parameter range not too far from current experiments. Early studies assumed that effects not described within the RWA could be experimentally observed by going from the optical to the microwave domain. In principle, the micromaser could be used for that purpose. We focus on atomic correlations, as the atoms exiting the micromaser cavity constitute the only physical entity that can be subjected to measurements. Within the RWA the only allowed transitions are the so-called energy-conserving transitions. We consider additional transitions which, despite being small, could give rise to measurable effects that we have investigated in the present work.