N-(3-Phenylpropionyl)glycine is an acylglycine.1 Urinary levels of N-(3-phenylpropionyl)glycine are increased in patients with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, an inborn error of metabolism characterized by intolerance to fasting, episodic vomiting, hypoketotic hypoglycemia, and dicarboxylic aciduria.