The Radiological Protection Institute of Ireland (RPII) monitors airborne radioactivity concentrations at ten stations throughout Ireland, of which nine are equipped with low volume particulate samplers and one, in Dublin, with a high volume particulate sampler. The low volume particulate samples are assessed for total beta activity. In the period 1998-2003 the total beta activity concentrations observed have been consistently low, ranging between 0.03 and 1.33 mBq m-3 with a mean over all sampling sites of 0.26 ± 0.15 mBq m-3 (n = 2361). High volume particulate samples have been assessed for caesium-137 and beryllium-7. A mean caesium-137 activity concentration of 2.3 ± 2.2 mBq m-3 (n = 26) was observed in samples taken since 1993 while the mean beryllium-7 activity concentration over this period was 3.0 ± 1.6 mBq m-3 (n = 42). In addition, air sampled at the RPII's laboratory in Dublin, is monitored for krypton-85, a radioactive noble gas, released into the environment primarily as a result of the reprocessing of nuclear fuel at installations such as Sellafield in the UK and Cogema La Hague in France. Analysis of the krypton-85 monitoring data, along with additional backward air trajectory modelling, demonstrate the influence of the reprocessing plants on the krypton-85 concentrations in Ireland.