Over recent years, physiologically based pharmacokinetic (PBPK) models have been used to better describe internal doses resulting from exposures to chemicals in the environment. PBPK models are mathematical descriptions of how chemicals are absorbed into, transported through, eliminated from, and stored in the body. More recently, physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models are being used to mathematically describe not only the disposition of a chemical in the body, but also how some normal biologic processes are altered as a result of the chemical in the body. PBPK/PD models should provide the ability to evaluate, estimate, and predict measures of toxicologically relevant doses. The Exposure Related Dose Estimating Model (ERDEM) is a PBPK/PD modeling system that was developed by EPA's National Exposure Research Laboratory (NERL). The ERDEM framework provides the flexibility either to use existing models and to build new PBPK and PBPK/PD models to address specific science questions. Over the past several years, ERDEM has been enhanced to improve ease of operation and to provide additional modeling capabilities. With these enhancements, ERDEM has been applied to a variety of chemicals as part of the regulatory risk assessment process. Applications for malathion and N- methyl carbamate were presented to and peer-reviewed by the FIFRA Scientific Advisory Panel. This report provides information on the use of ERDEM and related software.