This paper describes a single-subject study of vocabulary acquisition. The subject, an L1 English speaker, was required to learn 300 vocabulary items in Arabic at a rate of 15 new words a day over a period of 20 days. The learning period was followed by immediate and delayed tests of receptive and productive knowledge of target items. The immediate test results indicated knowledge of almost all the target items, but this acquisition was temporary, with evident attrition of both receptive and productive knowledge in subsequent test events. The paper considers factors which might affect the uptake and retention of items, and uses a matrix analysis to make long-term projections for vocabulary acquisition. (Contains 5 figures and 4 tables.)