This study investigates how a Second Language (L2) affects the use of the First Language (L1) in an environment where the main source of the foreign language (FL) is classroom instruction in which the target language culture is not directly present. The present study tries to answer a number of questions to show the L2 " L1 influence: (1) How will the conceptual system of L1 change under the influence of the L2? (2) How can this change be demonstrated in L1 production? (3) What elements of language production will give information on the conceptual change? Seventy-two Saudi university students (Ss) were randomly chosen as subjects for this research and were divided into two groups: (1) third and fourth year English major students and hence called bilingual (BILING) and (2) monolingual students with little English (henceforth MONO). The results have revealed some interesting findings. Overall, BILING Ss displayed signs of increased level of conceptual fluency as compared to their MONO peers. This can be seen clearly in the use of subordinate clauses where BILING Ss used almost double the number as compared to MONO Ss. The same thing can be said about their performance in the number and types of conjunctions. This result demonstrates that the BILING Ss’ group employs better use of the potential of the language and an increasing level of conceptual fluency in L1. The results have also shown that the BILING Ss’ group demonstrated the ability of use rich vocabulary and more freedom of conceptual use of the potential of the language. Thus, an increasing level of conceptual fluency was evident as compared to their MONO peers. In addition, English language has shown some positive effect on the performance of our BILING Ss’ group. In fact, the results of this study have shown that BILING Ss used sophisticated word types twice the frequency as often as their MONO counterparts. These results help point the way forward for future research in the area of L2 " L1 transfer.