To study the importance of changes in atmospheric pressure on radon entry into houses, we have simultaneously measured the soil-gas entry into an experimental basement structure and the fluctuations in atmospheric pressure. Small amplitude (~10 Pa), rapid (~20 min) fluctuations in atmospheric pressure were an important driving force for soil-gas entry because 1) the characteristic time for the propagation of a pressure disturbance in the soil gas was ~2 min, and 2) the time-rate-of-change of these small fluctuations is often larger than that of the semi-diurnal oscillations. An analytical model has been derived for a structure with a subslab gravel layer based on a one-dimensional solution to the transient pressure diffusion equation. This model correctly predicts the temporal response of the measured soil-gas entry into the experimental structure, but underpredicts the amplitude.