The changes of swimming patterns of spermatozoa accompanying capacitation were studied. The spermatozoa were seen to begin activated movement upon capacitation. The sperm activation was inhibited at low temperatures, in the absence of Ca²⁺, upon addition of Zn²⁺, and upon addition of Fr. I from guinea-pig spermatozoa which had decapacitation activity against rabbit spermatozoa. However, movement was not inhibited under the same conditions, when the spermatozoa had already acquired activated movement. It was apparent that the activation of spermatozoa was inhibited only when the prccess of capacitation was suppressed. Thus it is suggested that sperm activation is an inherent property of sperm capacitation.