The bilingual child is seen as a unique source of information about the relation between input and intake. The strength of the association between language exposure estimates and vocabulary learning was examined for 25 simultaneous bilingual infants (ages 8 to 30 months) with differing patterns of exposure to the languages being learned. Using the MacArthur Communicative Development Inventories, standardized parent report forms in English and Spanish, the percentage of all words that were known in each language was calculated and then plotted against the estimates of language input (also in percentages). A significant correlation was found, r(25)= .82, p < .001. The correlation was also strong when examined point-by-point, even for children whose language environments changed by more than 20%; between observations, although it was not reliable at lower levels of exposure to Spanish. Especially for children with less input in the minority language, the factors which appeared to affect the strength of the association between input and amount learned in a language are discussed.