Data from a transcript database of 12 children collected in 1-hour samples every month from 1;0 to 3;0 support the hypothesis that there should be strong differences in the frequency and types of errors between pronouns with suppletive nominatives and those without. The suppletive nominative forms "I" and "she" are blocked from overextension in a way that is not true of "he" and "they." (Contains 18 references.) (Author)