The vocalizations of 13 infants recorded weekly during their first year were examined. The focus was on the estimate of pitch and formant frequencies by means of Linear Predictive Coding (LPC). The study dealt especially with the development of general trends in the frequency parameters and the differences between cry and non-cry sounds. Around the 2nd or 3rd month of life there are striking modifications in the resonance features of the vocalizations. The frequencies of the first and second formant are noticeably lower, accompanied by a significant increase in their variability, particularly of the second formant. Because there are no reliable indications of reconfiguration processes in the vocal tract anatomy during this period which could cause these changes, the results are discussed in relation to the neuroanatomical and neurophysiological development.