The De Materia Medica of the Greek Dioscorides reports about 200 plants used for the treatment of pathologies of the urogenital tract during the 1st century AD. On the basis of explicit and implicit affirmations by Dioscorides, a theoretical system concerning the specific properties of these plants has been attempted. Comparison of the species reported by Dioscorides and Pliny the Elder for renal affections does not support the thesis of a close relationship between De Materia Medica and the Naturalis Historia.