Despite a number of research studies investigating the Yes-No vocabulary test format, one main question remains unanswered: What is the best scoring procedure to adjust for testee overestimation of vocabulary knowledge? Different scoring methodologies have been proposed based on the inclusion and selection of nonwords in the test. However, there is currently no consensus on the best adjustment procedure using these nonwords. Two studies were conducted to examine a new methodology for scoring Yes-No tests based on testees' response times (RTs) to the words in the test, on the assumption that faster responses would be more certain and accurate whereas more hesitant and inaccurate ones would be reflected in slower RTs. Participants performed a timed Yes-No test and were then interviewed to ascertain their actual vocabulary knowledge. Study 1 explored the viability of this approach and Study 2 examined whether the RT approach presented any advantage over the more traditional nonword approaches. Results showed that there was no clear advantage for any of the approaches under comparison, but their effectiveness depended on factors like the false alarm rate and the size of participants' overestimation of their lexical knowledge. (Contains 9 tables and 2 notes.)