A double-blind, randomized study tested the efficacy of steam (technically, heated, humidified air) inhalation in the treatment of common cold symptoms. Two 20-minute treatments spaced 60 to 90 minutes apart were given at the time of enrollment. The active device (Rhinotherm, Netzer-Sereni, Beer Yaacov, Israel) delivered 40 L/min of saturated air at 40 degrees C to 42 degrees C, while the identical-appearing placebo delivered 2 L/min of ambient air at 20 degrees C to 24 degrees C. There were 34 patients in the placebo group and 32 in the active group. Significant improvements in the placebo-treated group were obtained on subjective symptom scores for nasal congestion, nasal drainage, and sneezing on isolated days during the treatment period (40%, vs 25% on day 3, 71% vs 60% on day 6, and 100% vs 67% on day 7). Improvement in nasal resistance as measured by rhinomanography was better in the placebo group than in the active group on day 7 (11% vs -6%). Our study demonstrated no beneficial effects of steam inhalation on common cold symptoms.