Early vocabulary development in children lays the foundation for general language acquisition, including articulation, grammar and literacy. A great deal of recent research has shown the importance of early linguistic and communicative stimulation for word learning. The first phase of the SPRINT project at Stockholm University (“Effects of enhanced parental input on young children’s vocabulary development and subsequent literacy development”) aims to investigate the impact of a naturalistic family intervention on vocabulary development in Swedish children 18 to 36 months old. The general aim of the larger longitudinal study is to deliver a predictive model of environmental factors, including an education program for parents (the intervention), with emphasis on lexical development and subsequent literacy attainment, spanning the language development of children from 12 months through the first three years of school. The SPRINT project recognizes the importance of cultural context on language acquisition and is therefore part of an international network with representatives from seven countries aiming to share experiences and collaborate on comparative analyses of nation-specific data regarding children’s vocabulary development and reading acquisition. This will enable us to make international comparisons with the results of American studies such as Hart & Risley’s (1995) seminal work.Current analyses of data from the SPRINT project include an investigation of parental interaction style in relation to children’s vocabulary development. In this first study, a comparison is made of parental linguistic input directed to two sets of children chosen from the first intervention cohort. The two groups consist of children with low (0-25th percentile) and medium verbal ability (50-65th percentile) according to the Swedish version of the MacArthur CDI at age 1;6. Results, based on the analysis of audio recordings of parent-child interaction in four different everyday situations, indicate significant differences between the two groups of parents regarding the amount and diversity of input. In addition, the two groups of parents use positive interactive behaviors, such as affirming, imitating and commenting on their child’s communicative intent, to significantly different extents. The current analysis will be extended to include parental input by parents of children with high verbal ability at 18 months of age, the beginning of the three-month intervention period for the first of three intervention cohorts. The second and third cohorts started the intervention phase of the project when the children were 24 and 30 months of age, respectively. In addition, a statistical analysis of the vocabulary development of the children in the three intervention groups and a control group will be undertaken. A further extension of the project will be the development of a MOR grammar for Swedish, which will enable automatic morphosyntactic coding of material in the CHAT transcription format of the CHILDES database and thus facilitate computerized analysis of parent-child interaction. Current and future results of the longitudinal SPRINT project represent a unique opportunity for further research on children’s literacy development, from both a Swedish and an international perspective.