Large-amplitude harbor seiches usually occur in summer in the Balearic Islands. A significant correlation between sea level oscillations and atmospheric pressure disturbances has been found, though a proved physical mechanism to account for this atmosphere-ocean interaction is still missing. Using a flat bottom, shallow water model, we show that a direct coupling between atmospheric pressure and the free mode of an inlet is unlikely but that an oceanic wave of atmospheric origin can act as an intermediate mechanism and adequately force the inlet by resonance. The phase relationship derived from this mechanism is in good agreement with observations, provided the whole spectrum of oceanic waves is in opposite phase to the generating atmospheric disturbance. We also show that the very large oscillations observed at Ciutadella (an elongated, shallow inlet in the west coast of Menorca, Balearic islands) can be explained in terms of the particular shape of this inlet. ¿ American Geophysical Union 1993