Abstract: Datura metel is a plant that contains several different neurologically active phytochemicals which affect human health. On-going research has examined the potential role of the human neuroindoles, melatonin and serotonin, in medicinal plants with neurological efficacy. In this report, we describe the quantification of melatonin and serotonin in flowers and developing fruits of Datura metel and the effects of cold stress on the levels of these neuroindoles in the reproductive tissues of this plant. Melatonin and serotonin were found at the highest levels in the least developed flower buds with decreasing concentrations as the flower buds matured. Cold stress significantly increased the concentration of melatonin in young flower buds. In the developing fruit, melatonin was present at relatively stable, high concentrations for the first 10 days after anthesis. After 10–15 days, the ovule had grown to a sufficient size for excision and analysis and melatonin was found to be at the highest concentrations in the developing ovule with minimal concentrations of the neuroindoles in the fleshy fruit. Together, these data indicate that melatonin may play a role in protecting the reproductive tissues during flower and seed formation in a Datura species.