By means of non-invasive continuous blood pressure measurement (Finapres method), coefficient of variation for pulse rate (CV-PR) and coefficient of variation for blood pressure (CV-BP) under various respiratory conditions were calculated simultaneously to examine the interrelation between them. The subjects were 148 healthy normal adults and 75 patients with diabetes mellitus (DM). Both coefficients of variation for healthy normal adults showed significantly (p < 0.01) positive correlations: correlation coefficients tended to be greater during deep breathing than that during resting breathing. The case was the same for the ratio of CV-PR to CV-BP (CV-PR/CV-BP): the ratio for deep breathing was approximately 1.0. The ratio showed a significant decrease for DM patients compared with that for healthy normal group. The examination of the interrelation between these coefficients of variation under various respiratory conditions, which reflected the sensitivity of cardiovascular vagal reflex was considered to be also useful for the judgment of the degree of progress of DM-complications.