We present high-resolution He I 4471, Mg II 4481 and Hγ line profiles of the Be star 31 Peg obtained simultaneously at four observing dates. In this paper we focus on the He I 4471 line and on the absorption wings of the Hγ line which showed important variations. Models of static stellar atmospheres were calculated to determine the photospheric parameters of the underlying star. However, non-static and out of radiative equilibrium models are needed to better understand the structure of the atmosphere of 31 Peg and the characteristics of the observed He I 4471 and Hγ lines. The implication of deep atmospheric layers in the mass-loss phenomena of Be stars is suggested.