The paper presents the comparative analysis of the characteristics of environment, or input, in the native and foreign language acquisition. The available research provides contradictive data on the role of input in the said acquisition ranging from regarding it as a secondary factor because of its assumed deficiency to underlining the importance of the linguistic experience as the key to the development of grammar mechanisms. The proponents of the latter approach stress the role of the linguistic input, indicate that variable input affects acquisition, focus on the probable relation between the patterns used in input and those used by the language learners. They assume that the input structural complexity can determine the overall timing of the onset of specific language mechanisms. Even those who allow for the dependence of acquisition on the corresponding maturation mechanisms, consider the active interaction of the learner's internal grammatical system with the surrounding linguistic environment to be the most important component of language acquisition. The analysis of interim grammars of learners of English in a formal setting showed that they used similar sets of interim grammar rules, which could be represented in the form of substation tables (ST), The new students who joined the group later, initially had a different nomenclature of their interim rules but eventually tended to show signs of developing the patterns similar to the other learners in the group. This may be explained by the fact that the structure of interim grammar (ST patterns) depends upon the content and structure of the material processed by the students’ cognitive organizers. Identically organized input may contribute to the formation of similar (though not fully identical) interim grammar rules in the students’ minds. Consequently, the content and the structure of the input may have an impact on the configuration of intake, i.e. the part of the foreign language acquisition, which proceeds on the basis of the cognitive organizer’s operation and the subconscious development of grammar mechanisms.