OBJECTIVE The aim of this study was to examine the effects of D-myo-inositol-1,2,6-trisphosphate (alpha-trinositol) on haemodynamic variables and neuropeptide Y (NPY) levels in hypertensives and healthy volunteers. METHODS Hypertensives (n = 13) and normotensives (n = 11) were recruited after a screening of cardiovascular risk factors of all men aged 40 living in a well defined area. The hypertensives were previously unmedicated. The effect of alpha-trinositol was studied after intravenous infusion at rest, and during and after a maximal exercise test in a double-blind crossover manner with placebo. RESULTS Haemodynamic variables and NPY levels were recorded. NPY levels did not differ between normotensives and mild hypertensives at the start of the study. However, a significant increase was seen in hypertensives after they had risen to the sitting position. During exercise, the NPY levels increased significantly both in normotensives and hypertensives. After the exercise test, the NPY levels were significantly higher in hypertensives than in normotensives; alpha-trinositol did not modify these responses. In normotensives no significant difference in systolic blood pressure was seen during or after the exercise test whether they were on alpha-trinositol or placebo. In the hypertensives on active drug, however, the blood pressure tended to be approximately 5 mmHg lower during the exercise test as compared with the placebo group. In the hypertensives on active drug, the heart rate increased significantly more during exercise as compared with the placebo groups. In normotensives, the same tendency was seen, but it did not reach statistical significance. CONCLUSIONS The NPY antagonist, alpha-trinositol, tends to reduce the increase in systolic blood pressure induced by maximal exercise and increases the heart rate in hypertensives but not in normotensives.