We investigated the influence of biological immaturity and attachment security on linguistic development and tested whether maternal language mediated the impact of security on the child's linguistic abilities. Forty mother-child dyads were followed longitudinally, with the child's attachment security assessed at 24 months of age through trained observers' Attachment Q-Sorts, and linguistic abilities assessed at 24 and 30 months through observational measures and maternal reports. Both factors were found to contribute, though not independently, to the prediction of the child's linguistic abilities, and the mediation model was confirmed. (Contains 2 tables, 1 figure and 1 note.)