An experiment is described that is designed to test for the operation of an input switch mechanism in bilinguals. Their ability to selectively avoid processing words presented in one of their languages while they are attending to words presented in their other language is described. The 20 subjects were all French-English bilinguals. The specific method used was the flanker task, in which three vertically-arranged words are presented, the center word being the target and the two outside the flankers. Four types of flanker-target relationships were included. From the response times, it was concluded that the subjects were obliged to process the flanker words semantically, which suggests that bilinguals do not switch off the processing of words in one language even when they are engaged in processing words in their other language system. (EKN)