The technical note describes a computer code, PAID developed to determine time dependent dose rates and doses from inhaled or ingested radionuclides. The main purpose of this code is to determine the dose rates and doses caused by the intake of transuranic nuclides and their decay products. The two primary modes leading to internal radiation exposure are the inhalation and ingestion of radioactive materials. The estimation of organ burden and exposure, as well as of the resulting dose rates and doses, due to uptake by these pathways is relatively complicated and requires the adoption of mathematical models which depend on many parameters. A computer code which implements the lung model described by the ICRP Task Group on Lung Dynamics is presented below. This model has been augmented to also include the dose due to the transfer of radioactivity to other organs from ingested materials.