The release calls of Rhinoderma rufum (Philippi 1902) are described quantitatively based on recordings of four males of this species obtained in 1981 from a population in central Chile. This record corresponds to the last scientific sighting of the species. The release calls of R. rufum consist of sequences of complex notes containing harmonics and non-linear phenomena, with chaos segments and highly variable acoustic properties. This characterization expands the acoustic repertoire of this endemic and likely extinct species, and contributes to differentiating it from the extant congeneric R. darwinii.