Abstract: A radon sampling unit comprising a cylindrical body containing a measured amount of charcoal for collecting and holding radon gas. A fine mesh screen is frictionally held on top of the charcoal by a retaining ring engageable with the inner sidewall of said body. The lid is screw threaded and hermetically sealed to the body. A layer of dessicant is frictionally held inside the body vertically spaced above the charcoal. The cylindrical body has a plurality of alternate lugs on top thereof at different heights and a retaining metallic ring which serves as a unique method of retention of the lid assembly to the body. The cylindrical body may be modified by having an interior spirally wound metallic sheet to vary the inner diameter of the body as desired.