There is evidence that the rarefaction of the capillary bed is typical for the skeletal muscle of spontaneously hypertensive rats. We were therefore interested to learn whether there is also a rarefaction in skeletal muscle of human hypertensives. The number of capillaries was morphometrically analysed and counted in the quadriceps and the pectoralis major muscles of human normotensives (n = 12) and hypertensives (n = 15). The clinical diagnosis and certain pathological criteria, such as blood pressure (with or without antihypertensive therapy), heart weight, left ventricular wall thickness, the state of kidney arterioles and brain, and heart vessels, were used to classify the patients into two groups. The dissected tissue samples were prepared according to the GMA method and the capillary numbers per area were counted using light microscopy (250 x). The quadriceps muscle had a capillary density (per 2.5 mm2) of 442 +/- 51 in normotensives and 277 +/- 41 in hypertensive patients; in the pectoralis major muscle we counted 477 +/- 30 in controls and 232 +/- 28 in hypertensives. The rarefaction in the quadriceps muscle ranged by about 37%, in the pectoralis major muscle by about 51%. It is suggested that the reduction of the capillary surface area caused by the capillary rarefaction reduces the transcapillary fluid exchange and in that way prevents an overperfusion of the terminal vascular bed.