Radon activity concentration in outdoor air was measured using alpha radon monitors (Pylon AB-5 portable with Continuous Passive Radon Detector). Radon in outdoor air was measured in situ, in 5 points, for each lithological unit from the study area. The radon concentration was measured at a height of 15 cm above ground level. The radon exhalation rate was continuously measured for 24 hours with a counting time of 20 minute/interval in each site. The range is considerable: from 2.6 - 52 Bq m^-3. The release of radon from rocks and soil is controlled largely by the types of minerals in which uranium and thorium occur. In Ditrău Alkaline Massif, uranium (²³⁸U), thorium (²³²Th) and actinium (²³⁵U) are concentrated in accessory minerals such as: zircon, monazite, titanite, allanite, apatite, xenotime, rutile, thorite, bastnäsite, parisite, pyrochlore.