The spontaneous speech of two Zulu girls was monitored for use of nominals. The data for one girl, 23 months, are reported in detail. Analysis of prefixed and prefixless nouns in isolated citation forms and in syntactic construction revealed that the child perceived the internal structure of nouns before the age of two, although the prefix often did not occur in surface form. That prefixes were not arbitrary markers on the nouns in syntactic construction can be seen from an analysis of particular prefixes that occurred with noun stems. Of nouns occurring with prefixes, 77% appeared with the correct Zulu prefix for a given noun, as opposed to 23% that occurred with the wrong prefix. Correct prefixes appear to reflect an early lexicalization of prefixes with nouns. Sources within adult Zulu of the child's perception of systematic alternation of noun forms are numerous. The order of acquisition of noun class prefixes is detailed for a period in which the child progressed from a three prefix to a six prefix system. (Author/JB)