LDV has been modified to measure four microcirculatory responses in human nasal mucosa. Resting nasal blood flow was measured in 115 observations in 23 nonatopic subjects and 111 observations in 21 atopic subjects with allergic nasal disease. Other parameters measured concurrently were the number density of moving red blood cells (RBC), mean RBC speed, and flow pulsatility. Challenges with aerosolized buffered saline or water had no significant effect on any parameter. By contrast, nasal application of alpha-adrenergic agonists, oxymetazoline and phenylephrine, produced significant dose-dependent reductions in flow without any significant change in RBC number density. These results suggest a selective alpha-agonist effect on resistance vessels but not on capacitance vessels. Topical cholinergic stimulation with methacholine selectively reduced the RBC number density without affecting other parameters. These modifications of LDV may prove useful in analyzing nasal responses to provocation and determining the sites of action of vasoactive agents on the microcirculation.