This study investigates the effects of receptive and productive vocabulary learning on word knowledge. Japanese students studying English as a foreign language learned target words in three glossed sentences and in a sentence production task in two experiments. Five aspects of vocabulary knowledge--orthography, syntax, association, grammatical functions, and meaning and form--were each measured by receptive and productive tests. The study uses an innovative methodology in that each target word was tested in 10 different ways. The first experiment showed that, when the same amount of time was spent on both tasks, the reading task was superior. The second experiment showed that, when the allotted time on tasks depends on the amount of time needed for completion, with the writing task requiring more time, the writing task was more effective. If the second experiment represents authentic learning, then a stronger argument can be made to use productive vocabulary learning tasks over receptive tasks. (Contains 1 footnote.)