The IDEAS Guidelines [Doerfel, H.,et al. General Guidelines for the Estimation of Committed Effective Dose from Incorporation Monitoring Data. Report FZKA 7243, Forschungszentrum Karlsruhe, GmbH (2006); Castellani, C. M., Marsh, J. W., Hurtgen, C., Blanchardon, E., Berard, P., Giusani, A. and Lopez, M. A. IDEAS Guidelines (Version 2) for the Estimation of Committed Doses from Incorporation Monitoring Data. EURADOS Report 2013-01, Braunschweig (2013)] provide a structured approach to the assessment of intakes of radionuclides. In order to check that the guidelines, when applied to typical monitoring programmes, lead to reliable assessments, a number of numerically-generated datasets have been constructed and assessed using the guidelines. The dose and intake obtained by the assessment can be compared with the ‘true’ dose and intake. In this way, the accuracy of the IDEAS assessment process can be examined when applied to monitoring programmes that are typically used in the nuclear industry. The simulations focus on assessments carried out as a result of elevated 239Pu activities in routine urine samples, which lead to follow-up urine and faecal samples being provided. Cases where the assessor makes the correct initial assumption about lung solubility can be compared with cases where this initial choice is wrong. The results of these simulations and the implication for the use of monitoring programmes are discussed.