Spontaneous changes in middle ear pressure were measured tympanometrically in 15 healthy adults over 7.5 h under basal conditions. Despite fluctuation of middle ear pressure no temporal pattern existed and there was no evidence of reciprocal changes in pressure between sides. When awake but at rest the middle ear pressure fluctuates around ambient pressure. Recordings of positive pressure may represent supportive evidence in favour of a net basal tendency to produce a positive middle ear pressure.