The paper examines changes in the productive lexicon of advanced second language learners' writing over a period of one academic year. Sets of compositions of the same learners were analyzed in terms of lexical profile and lexical variation at three points of time. The analysis was performed by LFP (lexical frequency profile) measure, which classifies the vocabulary of an essay into frequency levels using a public domain computer programme developed for this purpose. Results indicate that there was some progress in lexical richness, but not in lexical variation. There was no correlation between the progress on the two variables. The results are discussed in terms of productive vocabulary development in a second language. Some teaching implications are suggested which relate to explicit vocabulary teaching as opposed to incidental vocabulary learning.