Several studies have questioned the validity of the C-test for measuring general language proficiency. This study investigates the feasibility of the procedure in a university foreign language major context. Recognising the importance of gathering information on test taking processes as part of construct validation, the think-aloud method was selected for data collection. The analysis of the introspective data comprised both quantitative and qualitative methods and was combined with classical item analysis. Results support earlier claims on the validity and reliability of the C-test, and provide evidence that in the given setting the C-tests under investigation can be a valid and reliable measure of most components of foreign language competence.