Physical and social interaction between humans and robots are important for humanoid robotics. In this article the characteristics of a handshake between humans are physically examined aiming at future experiments with a handshake between a human and a robot. A special pair of data gloves has been designed to measure quantitative characteristics of a handshake ritual such as duration, strength of the grip, and frequency of the rhythmic movements. Experiment results show that handshaking consists of four phases. After a physical contact, a mutual synchrony appears between the two persons. A statistical analysis shows that the frequency of this synchronization is around 4 Hz and average strength of the grip is 2.5 N.