Since the introduction of our plasma cortisol enzyme-linked immunosorbent assay (ELISA) [l] using affinity purified antiserum [2] into the routine steroid laboratory, we have embarked on the development of a simple urinary free or unconjugated cortisol ELISA which would allow measurement of both urine and plasma cortisol on the one ELISA plate. This paper describes for the first time an ELISA f...