Dynamic characteristics of the blood flow linear velocity in microvessels on the surface of rat's temporal muscle were determined by means of accelerated cinemicrography. The blood flow velocity varied from 200 to 5000 microseconds in microvessels with diameter 4-13 mu. The blood flow fluctuated with period of 0.3-7.0 sec and amplitude 0.5-100% of the average. Auto- and crosscorrelation analysis showed a positive interrelationship between velocities shifted in time by 0.5 sec in 37% of the cases. The interrelationships did not exist between rapid changes of the blood flow in either adjacent or distant microvessels. The sharp blood flow changes seem to be due to periodical passage of leucocytes and aggregated erythrocytes which increases the resistance of blood current in the microvessels.