Infant's crying may have an important mediating role in the formation of attachment behavior. The earliest vocalizations are discussed in terms of an acoustic communications model in which the baby's vocal repertoire becomes incorporated into a closed-loop, feedback system with his mother. Certain pre-lingual "signals" may be associated with those maternal actions which bring about a reduction in psychobiological stress, thus becoming one medium in which infant-mother attachments are formed. In order for a mother to determine a particular stressful state such as pain or hunger from the cry signal alone, crying would have to be acoustically distinctive to this state. To determine whether such distinctions exist, the vocalizations of twenty-two infants were tape-recorded under a variety of stressful conditions: pain stimulus, startle, evidence of hunger, etc. An ensemble technique of spectral analysis was developed to show that relatively long intervals of crying in one infant may indeed exhibit an average spectrum which is acoustically distinctive to the type of pain stimulus and to hunger. Less clear is whether such distinctions also transpose to groups of infants in a similar stressful state. (Author)