The continuous monitoring of ECG and intra-arterial blood pressure by the Oxford system was used in five ambulant patients for profiling autonomic reactivity during 24-h recording. This procedure overcomes, with minor invasiveness for the patients, the limitations represented by the discontinuous sampling of blood pressure. An original computerized procedure was used for obtaining, on a beat by beat basis, circadian rhythm and variability of R-R intervals and blood pressure. In selected parts of the 24-h recording, the values of blood pressure and R-R intervals were processed, during autonomic and cardiac tests, by means of correlation analysis. The results are consistent with the hypothesis that the orthoclinostatic test is a valuable method for the study of baroreceptor reflex in man.