Progress in the teaching of oral comprehension depends partly on the isolation of factors which block comprehension. Research in conjunction with an experimental course in English as a second language led to the definition of errors due to: (1) insufficient knowledge of the language and the cultural context of its use, and (2) a failure to recognize items previously learned. The present study focusses on the latter, and examines items learned in the areas of phonology, morphology, syntax, and semantics. It is found that errors in listening comprehension are caused by students' inability to deal with variation in English, or by external noise. The inability to deal with variation is attributed to the emphasis placed on writing skills, to the detriment of conversational skills. Emphasis on the written language gives an oversimplified impression of the language, and does not give the student the flexibility he needs in oral communication. Training in oral competence should therefore be introduced at a much earlier point in the curriculum. (CLK)