Thirteen Mexican-American children in Corpus Christi, Texas, most approximately six years old, were interviewed in Spanish for the purpose of establishing the phonology of their dialect. The linguistic competence of the children, not their performance, was of primary interest. A phonological chart was devised based on the data derived from the interviews. A certain amount of deviation was evidenced as a result of allophonic variation. Other deviations were found, however, that did not involve allophonic variation. These deviations can be grouped into the following six categories of phonological changes: 1) reduction of a consonant cluster; 2) insertion; 3) reduction; 4) vowel change, involving both assimilation and dissimilation; 5) consonant change, in which several specific types of substitution are apparent; and 6) metathesis. It is concluded that the Spanish-speaking first-grader in Corpus Christi is clearly capable of handling his own language. The traces of baby speech noted in this investigation suggest the possibility that the deviations are due partly to the lack of parental correction of speech patterns. However, the language development of these children can be determined only with more research. (LG)