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The advertisement calls of Melanophryniscus montevidensisand M. dorsalis, two red-bellied toads of the M. stelzneri group, are described for the first time. Melanophryniscus dorsalis is endemic to the coastal zone of southern Brazil (southern Santa Catarina and northern Rio Grande do Sul), whereas M. montevidensis has a parapatric distribution in the coastal regions of Uruguay and extreme southern Rio Grande do Sul. The calls of both species are similar to the published calls of M. atroluteus and M. stelzneri. The advertisement call of Melanophryniscus dorsalis differs from those of the other three species by a relatively high dominant frequency, long pulse duration and low pulse repetition rate. Although Melanophryniscus montevidensis and M. atroluteus are bioacoustically not well distinguishable, they are considered distinct species because of geographical separation and morphological differences, such as colouration and skin structure. All taxa are closely related and show great intraspecific variation in advertisement call and body pattern. Remarks on the taxonomy of the M. stelznerigroup are presented and a key for the identification of all known species is provided.