The goal of this research was to ascertain the effects of suprasegmental parameters (fundamental frequency, amplitude, and duration) on discrimination of polysyllabic sequences by 1- to 4-month-old infants. A high-amplitude sucking procedure, with synthesized female speech, was used. Results indicate that young infants can discriminate the three-syllable sequences [marana] versus [malana] when suprasegmental characteristics typical of infant-directed speech emphasize the middle syllable. However, infants failed to demonstrate discrimination when adult-directed suprasegmentals were used and in several other experimental conditions in which prosodic parameters were manipulated. The pattern of results obtained in the six experiments suggests that the exaggerated suprasegmentals of infant-directed speech may function as a perceptual catalyst, facilitating discrimination by focusing the infant's attention on a distinctive syllable within polysyllabic sequences.