The blood pressure of man is known to be modified by age, sex, posture, disease, drugs, the emotions, exertion and fatigue. From observations made by us during the annual physical examination of a group of officers of the navy, it appears that climate exerts a definite effect and that in the tropics the normal blood pressure, both of natives and of visitors from the temperate zone, is distinctly lower than in cooler countries. This physical examination of a group of naval officers was made in January on board ship in West Indian waters, and revealed the fact that blood pressure of the normal subjects of the group was from 10 to 15 mm. of mercury below our textbook1 standards. The systolic and diastolic pressures were about equally reduced. The average reduction in systolic pressure for sixty-seven officers was 11.4 mm. of mercury. The chart represents graphically the difference between