The volume adsorption capacity of activated carbon (Columbia type 4 LXC 12/28) at 20°C for 0.98 mol% argon is 0.109 ± 0.004 cm3 (STP) per gram of carbon. This determination is based on a measurement of the time-dependent transmission of argon in helium through an adsorber bed and on the analysis of that measurement in terms of a dispersion model. The transmission is the ratio of the concentration at the outlet of the adsorber bed to that at the inlet. The analysis yields values for the dispersivity as well as the effective adsorptivity. Both parameters are needed to calculate the steady-state transmission of radioactive argon.