The microcirculatory unit, which links arterioles with venules, is responsible for metabolic exchanges with the interstitial tissues and for the regulation of skin temperature. The sympathetic system controls cutaneous vascularization. A satisfactory method for dynamic clinical investigation of skin vascularization, previously not available, is now possible with the Doppler laser flowmeter which provides relative measurement of blood flow in the microcirculation. Three studies were conducted using this simple technique. Changes in skin blood flow were recorded in healthy volunteers during physiological stress: reactive hyperemia, hot and cold reaction test, respiratory changes, postural modifications. In patients with arteritis, the immediate effects of lumbar sympathectomy on skin blood flow were measured. During exploration of patients with vasomotor disorders, the cold test was performed by exposing the extremities in a thermal chamber: laser flowmeter recordings provided data on specific alterations occurring during a disease or Raynaud's syndrome. These findings will assist quantification of, and the application of predictive tests to the most useful measures to adopt for vasomotor disorders.