Aerosols, whether pre-existing in the atmosphere or generated in a nuclear incident, represent surfaces to which radionuclides that escape into the environment can become attached. The importance of the relationship between adsorbed activity and aerosol particle size is discussed. The conclusions from previous studies, most of which have utilized the decay products of radon and thoron as radionuclides, are contradictory. In the present work, a labelled iron oxide aerosol was allowed to interact with radionuclides consisting of molecular iodine. The Goetz Aerosol Spectrometer was used to characterize the adsorption of the iodine onto the aerosol as a function of particle size. Relative radioclide-aerosol concentrations were varied from 3 x 102 to 3 x 105molecules/particle. The following conclusions were drawn from these experiments first, the adsorbed activity appeared to be proportional to a function dz of the particle diameter, where 2< Z < 3, over the approximate size range 0.06 d < 1.2[mu]; secondly, even at the lowest radionuclide concentration used (9 x 10-6/[mu]gI2/1), some of the iodine seemed to be present in the form of very small particulates (<0.01 [mu]), a factor which complicated interpretation of the above result; thirdly, the adsorption of iodine onto surfaces was at least partially reversible; and finally, variation of the experimental conditions over a considerable range did not significantly affect the results.