A method, apparatus and computer program product are disclosed for non-invasively determining blood pressure of a subject. To improve the specificity of automatic blood pressure determinations in a patient monitor provided with a non-invasive blood pressure determination unit, a physiological index indicative of sympathetic activity is derived from a subject, variations in the physiological index are monitored, and the blood pressure determination unit is instructed to initiate blood pressure determination when the variations fulfill a predetermined condition.
