The motion of tissues within the human body can be investigated by a number of techniques, including ultrasonic echography. The ultrasonic echo patterns from regions of relatively homogeneous tissue bear an ambiguous relationship to their spatial structure, preventing the use of an lmaging system to study the motion of such tissue. This work describes the development and use of a method of analysing the ultrasonic echoes from tissue to investigate their motion. The properties of the echoes from tissue are studied using a theoretical model, and a number of methods of analysing the echoes are suggested. The theoretical model can also be used to simulate the ultrasonic imaging of such tissues. The apparatus for obtaining and analysing the echoes from tissues is described, with an investigation of the errors involved in the digitisation of analogue signals. The methods of echo analysis proposed for the study of tissue motion are evaluated experimentally, using specimens of fixed liver, and the results show that a correlation method of analysis provides the most consistent measure of tissue motion. This method is applied to the analysis of the in vivo motion of soft tissue. The majority of measurements are taken on the livers of normal subjects, with a simultaneous recording of the electrocardiograph. The amplitude, frequency and phase of the motion are measured and the results correlated with the electrocardiograph. The conclusions from this work are that the stochastic properties of the ultrasonic echoes from soft tissues require the use of statistical methods of analysis to study successfully tissue motion. Estimates are made of the extent to which the phenomenon of tissue motion can be used in the characterisation of the pathological state of tissue.