The purpose of this investigation is to determine whether a focused stimulation intervention focusing on lexical training has indirect, secondary effects on children's phonological abilities. Twenty-five toddlers with expressive vocabulary delays and their mothers were randomly assigned to intervention and control groups. The children were between 23 and 33 months of age at entry into the study and were at the single-word stage of language development. Parents of late talkers in the experimental group were trained to employ frequent, highly concentrated presentations of target words without requiring responses. Two measures of phonological diversity (i.e., syllable structure level and consonant inventory) and one measure of accuracy of production (i.e., percent consonants correct) were measured prior to and following intervention within the context of mother-child interactions. The toddlers who received intervention made treatment gains in two areas of phonological ability. They used a greater variety of complex syllable shapes and expanded their speech sound inventories to include more consonant sounds in both initial and final position. In contrast, there were no effects of language treatment on the accuracy of correct production when compared to the adult phonological system.