Non-invasive blood pressure measurement (NIBP) is one of the most discussed topic in cardiovascular medicine. Currently continuous measurement of blood pressure is possible by invasive methods, which makes the measurement impractical for Doctors and uncomfortable for the patients. It is possible to use special devices to measure blood pressure noninvasively continuously but there are still some problems with long time monitoring and comfort for patient. Physiologically there is connection between electrical and mechanical heart functions, propagation of pulse wave and blood pressure value. Our paper investigates various methods for the evaluation of NIPB from pulse transit time. We analyse real signals which we obtained during surgical interventions in Hospital, with invasive measurements of blood pressure waves, and non-invasive measurements of pulse waves and ECG signal.