Large neotropical hylid and leptodactylid frogs frequently emit loud distress calls under hand held conditions. In spite of remarkable similarities in the production and structure (i.e. spectral energy distribution, short rise and fall times) of these calls, distinct differences between the screams of the ten species studied were found. The percentage of adult individuals producing distress calls is high in Leptodactylus pentadactylus (60%), Hyla lanciformis (55%) and Hyla boans (42%). Screaming is far more common in large neotropical species than in their similar sized counterparts in Europe and North America. It appears improbable that distress calls in frogs have evolved as intraspecific warning signals. Startling an attacking predator and attraction of secondary predators capable of interfering with a threatening raptor are discussed as possible functions of distress calls.