This paper presents a brief summary of processability theory as proposed by [Pienemann, M., 1998a. "Language Processing and Second Language Development: Processability Theory." John Benjamins, Amsterdam; Pienemann, M., 1998b. "Developmental dynamics in L1 and L2 acquisition: processability theory and generative entrenchment." "Bilingualism: Language and Cognition" 1, 1-20; Pienemann, M., 2003. "Language processing capacity." In: Doughty, C.J., Long, M.H. (Eds.), "The Handbook of Second Language Acquisition." Blackwell, Oxford, pp. 679-714.] and reports on a small-scale study analyzing Japanese-speaking university students' oral performance in English. Pienemann argued that the second language acquisition process involves the acquisition of psychological processing procedures. The theory states that five processing procedures are implicationally related, defining the six stages of second language development. In order to test the validity of the theory, speech data were collected from seven learners of English as a foreign language (EFL). The participants performed five communicative tasks. Their speech data were analyzed in terms of interrogatives, word order, and negation. Results suggest that processability theory may be valid for Japanese-speaking EFL learners and that Japanese-speaking EFL learners produce interlanguage forms or structures that are predicted by processability theory. (Contains 5 tables.)