Old data reveal that the sensitivity and positive predictive value of CRP > 35 mg/L for the diagnosis of pneumonia was 100%, and lower values were reported for bronchitis and bronchiolitis, while more recent data demonstrate that CRP ≥ 20 mg/L were linked to radiographic pneumonia, bacterial infection, and subsequent hospitalization, yet positive predictive values were too low to be of use in clinical practice. The gene discussed is CRP; the disease is bronchiolitis.