Six dogs (Canis familiaris) were trained to sit and come reliably in response to tape-recorded commands. The phonemes within these commands were then changed, and the dogs' behavior in response to these modified commands was recorded. Performance markedly declined in all cases, with the type of alteration affecting response to the modified sit command but not to the modified come command. The results suggest that dogs do not perceive a tape-recorded command as simply a physical sound but that they recognize a relationship between certain sounds.