The nasal mucosa of 10 healthy volunteers was studied with the combination of rhinostereometry and laser Doppler flowmetry during a challenge with 0.14 ml histamine dihydrochloride in stepwise increasing concentrations of 0.5, 1.0, 2.0, 4.0, 8.0 and 16.0 mg/ml. Five and 10 min after each challenge the degree of congestion and the microcirculatory parameters perfusion, velocity of flow and concentration of moving blood cells were recorded. A complex reaction pattern was seen. It was possible to measure simultaneously the degree of congestion and the microcirculatory parameters. With this combination of methods, it seemed possible to identify the effects of histamine on the different components of the nasal mucosa. The combination of the two methods appears to make possible detailed studies of the relationship between changes in congestion and microcirculation during intranasal challenges in humans.