Part 1. Findings in Normal Subjects. Two types of rotatory examination, cupulometry and threshold-latency method, were performed and normal values were obtained with regard to the duration of post-rotatory nystagmus, the latency and the threshold of per-rotatory nystagmus. Nystagmus was observed behind Frenzel's spectacles. Fifty "apparently normal" test-subjects (among them, seven were ballet-dancers) were examined in this study. Rotatory stimulation was given by means of an electrically driven rotating chamber which is constructed so as to be easily controllable at any needed angular acceleration or deceleration, as well as at any needed angular velocity. Sudden but smooth stoppage of this chamber is possible, too. The results obtained were as follows:- 1) Nomograms predicting the normal limits of variation of cupulogram were presented. 2) Normal value of the latency of nystagmus was about four seconds (4.3"±3.7"). 3) The threshold of nystagmus in normal subjects was found between 0.3"∼0.75"/sec2. In, cases of ballerinas, the threshold was found within the normal range, but with a slight elevation of the threshold. These results led us to the conclusion that, when the subjects, are examined who used to receive repeated rotatory stimulation in their daily life, the vestibular reaction is depressed, when expressed with the duration of post-rotatory nystagmus, On the other hand, however, in these cases, no distinct disparity from normal values can be observed regarding the latency and the threshold of nystagmus. Statistical difference between reactions of the labyrinths on both sides was not remarked regarding the duration, the latency and the threshold. Part 2. Findings in Patients. Vestibular examination was performed on 63 pathological cases (33 cases with peripheral vestbular lesions, 30 with central ones) who visited the ear-nose-and-throat clinic in our hospital with chief complaints of vertigo and disturbances of equilibrium during these two years. The results obtained in these cases led us to the following conclusions: 1) Comparison between per- and post-rotatory examination With regard to the ability to discover either the laterality and/or the abnormality of vesti- bular function, per-rotatory test was found surpassing post-rotatory one. Threshold-test had an ability to indicate the affected side in cases of acoustic tumor and Meniere's disease etc., and, moreover, allowed to determine quantitatively the extent of the vestibular deficit. Latency-test appeared to have the same .characteristics but seemed to be inferior to threshold-test in its ability to indicate the side of the lesion. 2) Comparison between rotatory test and caloric test In more than half the cases, whose threshold of per-rotatory nystagmus was regarded within normal values, caloric test could reveal pathologycal findings. This must depend upon the fact that, contrary to caloric test, rotatory test stimulates. both labyrinths at a time and also the fact that a compensatory action of the central nervous system participates more easily in the mechanism of nystagmic reaction. Consequently, when one attempts to detect "laterality" of the periphetral labyrinth, caloric test is regarded to be more usefull and valuable than rotatory one, if applicationof the former is only possible.