Androstenedione is produced by the adrenals and gonads. As a result, the determination of the level of androstenedione in serum is important in the evaluation of the functional state of these glands. Androstenedione is a precursor of testosterone and estrone. Besides the adrenals, in females, the ovaries have been shown to be an important source of androstenedione. It has been reported that there is a fluctuation day by day of androstenedione during the ovulatory cycle. The use of serum testosterone determination in conjunction with the enzyme immunoassay of androstenedione can be used to determine if the source of the excess androgen production is adrenal or ovarian.