(+)-Biotin 4-amidobenzoic acid is a biotinidase substrate. Upon enzymatic hydrolysis, 4-aminobenzoic acid (PABA; ) is released which can be quantified by colorimetric detection at 540 nm in the presence of N-1-naphthylethylenediamine as a measure of biotinidase activity. (+)-Biotin 4-amidobenzoic acid has been used in the evaluation of biotinidase deficiency, an inborn error of metabolism characterized by ketolactic acidosis, hyperammonemia, and neurological dysfunction.