A major requirement for theory development in L2 vocabulary acquisition is anadequate model of L2 lexical organization and processing. At present, there is no widelyaccepted model of this kind, but recent research has demonstrated the potential usefulness ofLevelt's (1989, 1993) L1 speech processing model (de Bot & Schreuder, 1993;Green, 1993; Poulisse, 1993). This paper explores the relevance of the model as adapted for L2lexical processing of written texts, with particular attention to its mental lexicon components(concepts, lemmas, and lexemes) and organization. The model is first discussed in terms of itsrelevance to L2 lexical access, retrieval, and acquisition processes. Findings of an introspectiveL2 vocabulary study follow, detailing how university ESL learners reported dealing withunfamiliar words while carrying out L2 reading tasks. The information provided on their lexicalinferencing strategy and varied knowledge sources used in the process provide support for thelexical components and organization proposed by Levelt. It is argued in this paper that theprocess of inferring the features of unknown words in a reading passage can be described interms of lemma construction, as defined in the model.