The Food and Drug Administration (FDA or Agency) is announcing the availability of a revised draft guidance for industry entitled “Inborn Errors of Metabolism That Use Dietary Management:  Considerations for Optimizing and Standardizing Diet in Clinical Trials for Drug Product Development.”  This draft guidance describes FDA’s current recommendations for optimizing and standardizing dietary management in clinical trials for the development of drug products intended to treat inborn errors of metabolism (IEM) when dietary management is a key component of patients’ metabolic control.  Optimizing and standardizing dietary management in these patients before they enter clinical trials and during clinical trials is essential to providing an accurate evaluation of the efficacy of new drug products.  This guidance revises the draft guidance of the same name issued on July 24, 2018.