The spatial and temporal variation of air-borne 222Rn concentration was continuously measured during 1990-94 with monthly changed etched track detectors in the Pál-völgy and Mátyás-hegy caves, Budapest, Hungary in order to identify site-specific behaviour of radon variations. We found winter minimum and summer maximum levels at each measuring site. In the Pál-völgy cave these end values increased with the distance from the entrance. The maximum-to-minimum
ratio, however, showed a broad peak between the entrance and deep cave region. This behaviour can be attributed to the seasonal and depth dependence pattern of the advective dilution effect caused by intrusion of outside radon free air. Far from the entrance radon concentration goes to a saturation value, which approaches the level found in a highly unventilated remote cavity of the cave. In the Mátyás-hegy cave the maximum-to-minimum ratios were small and nearly constant, indicating that the measuring sites belong to deeper parts of the system. The higher maximum
values, on the other hand, are attributed to smaller passage sizes of this part. High similarity was found in the temporal variation of radon concentration in the
neighbouring parts of the two caves, which reinforced the assumed but by man unpenetrable connection between them
