The primary function of the nose is to warm and humidify air. We have previously shown that raising nasal mucosal temperature by immersing feet in warm water increases the amount of water evaporated by the nose as air passes through it (nasal conditioning capacity; Abbott D, Baroody F, Naureckas E, and Naclerio R. Am J Rhinol 15: 41-45, 2001). To investigate further the effect of nasal mucosal temperature on nasal conditioning capacity, we raised the temperature through alpha-adrenoreceptor blockade by intranasally administering phenoxybenzamine. We hypothesized that blocking alpha-adrenoreceptors during inhalation of cold, dry air would lead to an increase in nasal blood flow, surface temperature, and nasal conditioning capacity, as measured by the water gradient. After appropriate pilot studies, we performed a double-blind, placebo-controlled, two-way crossover study in nine nonatopic, healthy subjects by studying the effect of treatment with intranasal phenoxybenzamine. Nasal mucosal temperature increased significantly after administration of phenoxybenzamine and was associated with a significantly smaller net decrease in nasal mucosal temperature after exposure to cold, dry air (P < 0.05). However, there were no significant differences in nasal conditioning capacity between treatments (P > 0.05). Phenoxybenzamine decreased the symptom of rhinorrhea after exposure to cold, dry air (P < 0.05), but congestion was not different between individuals given phenoxybenzamine and placebo (P > 0.05). Our data demonstrate that phenoxybenzamine, despite raising mucosal temperature and not affecting nasal volume, did not affect the ability of the nose to warm and humidify air.