The transfer parameters of a new age-related model for plutonium metabolism, which have the largest influence on urinary excretion, are determined by applying a sensitivity analysis and assuming a direct uptake into blood. Realistic cases of contamination via ingestion and inhalation were considered as well and sensitivity coefficients for non-systemic parameters were calculated. The most important parameters in relation to the path of intake are identified and the effects of the modifying factors proposed by the ICRP in the case of alteration of respiratory tract physiology are briefly examined.