This investigation was designed to examine the acquisition of a set of complex English structures by Egyptian Arabic-speaking adult learners at different levels of proficiency. Two studies were conducted using the methodology of Chomsky as adapted by d'Anglejan and Tucker. In addition, some subjects were asked to translate a number of stimulus sentences to probe explicitly for evidence of interlingual interference. The results for the more advanced learners indicated a developmental pattern similar to that reported by Chomsky for child native speakers. All subjects appeared to deal directly with the linguistic data of the target language. No evidence was found that they attempted to translate or to map native language structures onto those of the target language (Author)