Developmental changes in the prosodic features of infant vocalizing were studied with novel electroacoustic techniques. Complete and continuous recordings of all the vocalizations of two infants during the first five months of life were collected, beginning with the birth cries and continuing uninterrupted as the infants were moved into plexiglass “air-cribs” at home. These recordings were systematically sampled for analysis. The prosodic features of vocalizing were analyzed by extracting three acoustic parameters: fundamental frequency (Hz), amplitude (dB), and duration (msec) during each of the 108 samples. The outputs of the parameter extractors (analog electronic devices) were measured every 25 msec by an analog-to-digital converter, then processed by an on-line digital computer. Composite statistics, describing the three prosodic features of the vocalizing in each sample, were plotted separately as a function of age at the time of sample. Parameter values and trends in the prosodic features of infant vocalization are reported.