Ten healthy subjects and 10 patients suffering from allergic rhinitis to birch pollen were investigated with the combination of rhinostereometry and laser Doppler flowmetry, thus simultaneously measuring changes in mucosal swelling and microcirculation, following intranasal histamine challenge. Compared to normals, the allergies had a higher degree of congestion and a lower increase in perfusion and velocity of flow. In the allergies there was a decrease in CMBC (concentration of moving blood cells) that was not seen in normals. The decrease in CMBC seen in allergies could be attributed to an increase in vascular permeability producing an interstitial edema, a well-known effect of histamine. After treatment with 1 week of intranasal steroid, most of the differences in the reaction pattern between normals and allergies had disappeared.