This study examined the relationship between learners' incidental vocabulary acquisition and their level of proficiency, and between acquisition and word frequency in a text. Participants were Turkish learners of English at three proficiency levels. One reading text and four vocabulary tests were administered over a two-week period. Analyses of the data revealed that lexical gains from reading were significant for each group (p less than 0.05). The higher proficiency groups were able to acquire more words than lower level groups. Word frequency in the text was also a significant factor in vocabulary acquisition (p less than 0.05), with 29% of the variance in acquisition being accounted for by frequency. However, frequency did not play a greater role in the vocabulary acquisition of lower level learners than in that of higher level learners. (Contains 1 note, 8 tables and 4 figures.)