In a study of 20 preterm infants--10 of low socioeconomic status" (SES)--and 33 full-term infants--16 of low SES--from 0;4 through 1;6, premature infants showed reliably less mature vocal patterns than their full-age mates. Premature infants were indistinguishable from full-term infants matched for gestational age in infraphonological development. Middle and low SES infants were statistically indistinguishable in ratios of speechlike vocalizations. (45 references) (JP)