Although it may seem surprising that a viral etiology was not identified in Ͼ40% of children with cold symptoms using the most sensitive molecular techniques currently available, the definition of a "cold" is actually somewhat nebulous (9) . In one study of 215 adults who reported they were developing a cold, only 54% had at least one respiratory symptom and only 17% met Jackson criteria for a cold (23) . Thus, the use of a "clinical cold" as the entry criterion for clinical trials on the efficacy of a potential viral URI treatment includes participants with heterogeneous clinical conditions and may bias findings toward the null if the therapy being tested is specifically acting by an antiviral mechanism. If a symptom scoring system could more reliably predict a viral URI, analysis of data from clinical studies could be conducted to assess efficacy in the subset of patients with a probable viral etiology. This approach would have the benefit of decreasing heterogeneity of the sample and eliminating the need for expensive laboratory testing to confirm viral etiology in clinical studies.