Results from a number of studies of human empathy are interpreted as demonstrating that young infants exhibit concern towards others who are suffering. Studies of empathy in young infants, however, often confound interest in intensity and ecologically valid stimuli with concern about others' suffering. Using a perceptually controlled design with ecologically valid stimuli, we investigated whether very young human infants preferentially look at a peer in distress. We showed 78 3-6-month-old infants videos of four babies who were crying and cooing along with synthetically generated control videos of the same babies that preserved their perceptual features. Results showed that infants overwhelmingly looked longer at babies who were crying versus cooing, with the same relative difference observed for crying versus cooing controls, although infants found real babies more interesting than controls. Results suggest that infants' attention to differences in emotional valence related to empathy cannot be clearly interpreted without controlling for associated perceptual differences.