Clinical measurements are widely used to evaluate both the severity and outcome of acute and severe episodes of wheeze. A large number of clinical scores have been produced, rating the severity from 0 to 3 or 4. The heterogenicity of these clinical scores, their subjective nature, shown by the poor interobserver agreement and the poor correlation with oximetry, make comparison between trials very difficult. Other clinical indicators, such as duration of hospitalization, maximum inspired oxygen fraction (FI,O2) and need for additional treatment, may be confounded by factors other than the wheezing episode. In contrast, provided standardized methods are used, respiratory rate, oxygen saturation and arterial blood gases are objective measurements and valuable tools. In order to evaluate the effect of interventions it is necessary to undertake a systematic evaluation of clinical variables: Which variables have the least interobserver error? Which variables are the most discriminant? New techniques, such as acoustic measurement, cough recording, respiratory inductive plethysmography (quantifying thoracoabdominal asynchrony and derived timing indices) should be developed and validated.