Die Erfindung betrifft die Verwendung von Phosphonoameisensäure, deren Hydrate sowie deren pharmazeutisch verträglichen Estern und/oder Salzen zur Herstellung eines Arzneimittels zur Behandlung von Tumorerkrankungen und/oder altersbedingter Makuladegeneration.Use of phosphonoformic acid or its hydrate, ester and/or salt for treating tumor diseases and/or age-related macular degeneration, is claimed. An independent claim is included for phosphonoformic acid or its hydrate, ester and/or salt for treating tumor diseases and/or age-related macular degeneration. ACTIVITY : Cytostatic. MECHANISM OF ACTION : None given.