Objective: In accord with the notions of humoralism that prevailed in medieval medicine, therapeutic interventions, including diuretics, were used to restore the disturbed balance among the four humors of the human body: blood, phlegm, yellow bile, and black bile. Most diuretics were derived from plants. The primary textual reference on herbal diuretics was Dioscorides's De Materia Medica, which was written during the first century CE. Design: The authors reviewed the medieval medical texts written in Persian and Arabic and compiled a list of 135 herbal diuretics used by the medieval medical authorities for treating various ailments. Results: Between the 8th and 11th centuries CE, Middle Eastern physicians systematically reviewed extant books on medicine and pharmacotherapy and compiled new and expanded lists of herbal medicines, diuretics in particular. Furthermore, they introduced new chemical methods of extraction, distillation, and compounding in the use of herbal medicines. Conclusions: Several herbal remedies now are considered as potentially safe and affordable alternatives to chemical pharmaceuticals. Thus, research on medieval herbal therapies may prove to be relevant to the practice of current cardiovascular and renal pharmacotherapy. The authors propose that modern research methods can be employed to determine which of these agents actually are effective as diuretics.