The estimation of acetanilide and its metabolic products, aniline, N-acetyl p-aminophenol and p-aminophenol (free and total conjugated) in biological fluids and tissues.

Brodie and Axelrod confirmed that paracetamol, also known as acetaminophen, was the major metabolite of acetanilide in human blood, and established that it was efficacious an analgesic. Unlike its precursors, paracetamol does not cause methemoglobinemia in humans. See also their follow-up papers:  "The fate of acetanilide in man" (PDF). J. Pharmacol. Exp. Ther., 94 (1948) 29–38., and Flinn, Frederick B., Brodie, B. B., "The effect on the pain threshold of N-acetyl p-aminophenol, a product derved in the body from acetanilide", J. Pharmacol. Exp. Ther., 94 (1948) 76-77.