In the last few years much attention has been drawn to the mast cells because they contain substances with a marked biological effect. These cells, which belong to the cellular elements of connective tissue, were discovered by Ehrlich (1879), who presumed that they were related to the digestion and therefore named them mast cells. They contain large granules containing substances which play a great part in inflammatory and allergic reactions. This is to report a study made on the appearance of tissue mast cells in tongue, esophagus, stomach, small intestine, large intestine and the skin of albino male rats after rotatory movement. The experimental animals utilized were healthy albino rats weighing from 120 to 130 gms, and they were divided into the following four groups according to the various experimental procedures. 1) Normal group : Without any procedure. 2) Control group : Same preparative procedure as for rotation, but without rotation. 3) 30 rotation group : 30 angular rotation per minute for one hour. 4) 60 rotation group : 60 angular rotation per minute for one hour. After the various procedures, the animals were sacrificed after intervals of 0, 1, 2, 4, 24, 48, 72 hours, 4 days and 7 days. The paraffin sections were prepared and stained with toluidine blue to demonstrate the tissue mast cells. The mast cell count was made covering 20 high power fields in each section and the findings in the different parts compared. The results of the study are summarized as follows ; 1) The distribution of tissue mast cells observed in various areas in the normal group showed the highest number in the skin and tongue tissue. (171.1±10.62 and 143.1±12.99 respectively per 20 fields) Next in order was the stomach, esophagus, small intestine and large intestine. 2) In the control group a slight decrease was demonstrated in the various tissues after one hour with recovery to normal values after two hours. 3) The average number of tissue mast cells observed in various area in the 30 rotation group showed a sudden decrease after rotation and reached its minumum after 2 hours with gradual recovery to normal values after 48 hours. 4) In the 60 rotation group there was also a sudden decrease after rotation reaching its minimum after 4 hours with recovery to normal values after 4 days, but the average number of mast cells was considerably less than in the 30 rotation group. The time for recovery to normal values was parallel to the numerical decrease, that is to say the more pronounced the decrease was, the longer was the recovery time. 5) The changes in the amount of mast cells after rotatory stimulation showed a percentual bigger decrease in tissues such as stomach and esophagus. The next in order was the small intestine and large intestine but the decrease was less pronounced in the skin and tongue than in other tissues. 6) The decrease of mast cells after rotational stimulation, was attributed to the normal mast cells, while the degranulation form on the contrary was increased. During the recovery to normal the percentage of the normal form increased and the degranulating form decreased to return to normal values. 7) The change in the number of the tissue mast cells of the digestive organ and skin by accelerated rotation could be suspected to be secondary to a functional disturbance in the autonomic nerve system caused by the labyrinthine stimulation.