Redundancy in language reduces the possiblity of error and permits communication where there is interference in the communicating channel. The relationship between creativity (the basic distinction between language-like behavior and knowing a language) and redundancy has been clearly established. Knowledge of rules is the key factor in creativity and is also the principal factor in the understanding of messages with reduced redundancy. In this paper the author discusses the three techniques that have been employed to test a subject's ability to function with a second language when noise is added or when portions of a test are masked. They are the cloze, clozentropy, and the noise tests. In the cloze test, portions of a written or oral test are blanked out and the subject is called on to provide the missing word or words. The clozentropy procedure measures a subject's performance in terms of a group norm. Thus, foreign students are scored according to the extent to which their responses agree with the normal responses of native speakers. The noise test originally consisted of a number of sentences to which noise had been added at signal to noise ratios of 1, 4, 7, 10, and 50 decibels. Recently, a multiple choice version has been prepared. The author feels that these practical studies have shown the value of language testing techniques based on redundancy. (DO)