This paper is an illustrative report on a study about 'weak forms" which were investigated especially from the standpoint of learning and teaching in language laboratories. The investigation was mainly based on some analyses of the test results obtained in the course of carrying out LL classes to totally 97 university students for four academic years (1972-'75). The results were as follows: (1) there existed a significant correlation between the perception ability of "weak forms" and the comprehension ability (r = 0.889, N 69), (2) it was possible even for university students to learn "weak forms" effectively by the method of dictation practice in a language laboratory for about 20 mins. every week during one semester, and (3) the learning process could be eventually observed by an error analysis, and the assumed process may be applied to the future systematic teaching and training program. Finally we also suggest a tentative way of systematizing a teaching program in the LL by making use of the computer.