The aims of this study were to: (1) investigate the effectiveness of teaching machines in teaching vocabulary, (2) examine the relationships between various anxiety levels and the effectiveness of the teaching machine and the relationships between extroversion and introversion and the effectiveness of the machine, and (3) examine the possible interaction effects between the various personality characteristics and the effectiveness of the teaching machine in the teaching of vocabulary. A sample of 149 students was divided into two treatment groups and one control group. Treatment I consisted of the use of the Non-Linear Systems Vocabulary Builder; Treatment II involved the use of vocabulary programed booklets; Treatment III, the control group, was to do the kind of vocabulary work that is normal work in an English class. All were subjected to the Ginn Diagnostic Vocabulary Test as a pre-test, a post-test, and a follow-up test one month later. Treatment I showed a significantly higher gain in vocabulary acquisition, and showed a slight, but statistically non-significant loss on the follow-up test of retention. Treatment Group II showed a slight gain on the post-test and made a gain on the follow-up test. The control group showed a slight gain on the post-test, but a significant gain on the follow-up test of retention. Further research is recommended to determine the reason for the rise in scores between post-test and follow-up test. (Author/CK)