Vocabulary scores, word span, nonword repetition, rhyme detection, and articulation rate measures were obtained for a group of 30 preschool children with a mean age of 4;11. After allowing for age and intelligence, it was found that the best predictors of vocabulary were memory span, rhyme detection, and nonword repetition, accounting for 19%. 15%, and 13% of the variance, respectively. Of these children, 28 were tested again on the same measures 13 months later. At the later stage, memory span and rhyme scores again predicted vocabulary to a significant extent, but nonword repetition score did not. Of the measures taken initially, memory span and rhyme detection significantly predicted later vocabulary scores, whereas nonword repetition just failed to reach significance. Cross-lagged correlations showed (hat memory span and rhyme detection on the first test predicted later vocabulary after partialing out initial vocabulary scores. However, initial vocabulary scores did not predict later memory span (or rhyme detection) after partialing out the initial span (or rhyming) scores. Articulation rate was not significantly related to vocabulary at either age. The results are interpreted as indicating that the phonological store of working memory (required by word span, rhyme detection, and nonword repetition, but independent of articulation rates) contributes to vocabulary development.