Closants, or consonantlike sounds in infant vocalizations, were described acoustically using 16‐kHz spectrograms and LPC or FFT analyses based on waveforms sampled at 20 or 40 kHz. The two major closant types studied were fricatives and trills. Compared to similar fricative sounds in adult speech, the fricative sounds of the 3‐, 6‐, 9‐, and 12‐month‐old infants had primary spectral components at higher frequencies, i.e., to and above 14 kHz. Trill rate varied from 16–180 Hz with a mean of about 100, approximately four times the mean trill rate reported for adult talkers. Acoustic features are described for various places of articulation for fricatives and trills. The discussion of the data emphasizes (1) dimensions of acoustic contrast that appear in infant vocalizations during the first year of life, and (2) implications of the spectral data for auditory and motor self‐stimulation by normal‐hearing and hearing‐impaired infants.