Melatonin is a hormone secreted by the pineal gland in the brain. It helps to regulate other hormones and maintains the body's circadian rhythm. The circadian rhythm is an internal 24-hour “body clock” which plays a critical role in the sleep-wake cycle. When it is dark, the body produces more melatonin; when it is light, the production of melatonin decreases. Commercial kits are available for ELISA and RIA, but are either not sufficiently sensitive or are complex and expensive to run routinely.

A highly sensitive, robust, picogram level LC-MS/MS method for the determination of melatonin was developed. The method was fully validated to current regulatory standards and used to support clinical studies.