Systolic blood pressure of a subject is determined by application of monotonic changing pressure conditions over a region of an organ of the subject, simultaneous illumination of a tissue in the pressurized organ with light and measurement of optical data indicative of passage of the light through the tissue and of pressure data indicative of the pressure being applied over said region of said organ. At least one pulsatile and at least one baseline component are determined from the measured optical data and changes are then identified in each of the components, said changes indicative that the pressure applied over the organ is smaller than a systolic blood pressure of the subject. The systolic blood pressure of the subject may be determined as a maximal applied pressure at which at least one of the changes in the pulsatile component and the changes in the baseline component started to appear.
