Literature data from in vivo chest measurements and urinary excretion rates of individuals exposed to U3O8 and UO2 were used to compare the results predicted by different models with empirical observations in humans. As a result the use of the respiratory tract model proposed in ICRP Publication 66 with its default absorption parameters underestimates urinary excretion of inhaled U3O8 and UO2. The new respiratory tract model also overpredicts the Fecal/Urine activity ratio, independently of the systemic model. For U3O8 and UO2 the choice of systemic model has very little influence on the predicted urinary excretion of inhaled compounds. On the other way, the choice of the respiratory tract model does influence the predicted urinary excretion significantly. In this work specific absorption parameters for U3O8 and UO2 were derived to be used in the respiratory tract model proposed in ICRP Publication 66. The predicted biokinetics of these compounds were compared with those derived for Type M and Type S compounds of uranium.