abstract the variables affecting the nature of reading comprehension can be classified into two general categories: reader’s variables, and text variables (alderson, 2000). despite the wave of research on vocabulary knowledge as reader’s variable, the role of this knowledge in c-test as a text-dependent test and its interaction with lexical cohesion of the test as a text feature has remained an under-researched issue. the purpose of this study was threefold: first, the role of breadth and depth of vocabulary knowledge as reader’s variables in efl learners’ c-test performance was examined. second, the effect of lexical bonds and readability indices as text variables was probed. third, the interaction of these variables was studied to find how they can contribute to the test takers’ c-test performance. for this purpose, vocabulary levels test (vlt) and word associates test (wat) were administered to 50 lower-intermediate and 85 upper-intermediate efl students. the participants then took a c-test with two sub-tests, one with high and the other with low lexical bonds determined by hoey’s (1991) lexical cohesion analysis and wordnet online dictionary. the sub-tests were also monitored to have high and low readability indices but all of which had average lexical difficulty determined by adelex analyser tool. the results indicated that: (a) depth of vocabulary knowledge could not affect c-test performance of lower-intermediate students but it affected the performance on high-bond c-test for the upper-intermediate students, (b) breadth of vocabulary knowledge did not affect the performance on c-test for neither upper-intermediate nor lower-intermediate students, (c) the interaction of breadth and depth could not influence c-test performance, (d) performance on vocabulary breadth contributed to the prediction of efl learners’ c-test performance and its two sub-tests for both lower and upper-intermediate levels, (e) breadth of vocabulary knowledge contributed to the prediction of c-test performance and its two sub-tests for lower-intermediate students while for upper-intermediate students, both breadth and depth of vocabulary knowledge predicted the performance, (f) depth of vocabulary knowledge predicted the performance on high-bond c-test for upper-intermediate students while breadth of vocabulary could not, which means more proficient students can make use of contextual cues while lower students may not, (g) lexical bonds significantly affected efl learners’ c-test performance at both lower and upper-intermediate levels, and (h) readability indices were found to be inadequate determinants of text difficulty level. the findings have pedagogical implications for students, teachers and materials developers to concentrate more on aspects of vocabulary knowledge especially depth of vocabulary. furthermore, the results draw test designers’ attention to the significance of lexical cohesion as a determinant of text difficulty and inadequacy of readability indices. keywords: lexical cohesion, lexical chain, lexical bond, breadth of vocabulary knowledge, depth of vocabulary knowledge, reduced redundancy principle, c-test