The prognostic relevance of an enhanced variability of peak expiratory flow rate (PEFR) throughout the day was evaluated in asthmatics in remission: it was expressed as the coefficient of variation (CV) of values recorded 4 times daily for 2 weeks. Outcome at 3, 6, and 12 months was assessed in 2 groups of 16 patients each, differing because of a CV respectively higher (group A) and lower (group B) than 8%. A significantly higher frequency of abnormal PEFR values during the subsequent 3 months was recorded in patients of group A, and found as correlated to the magnitude of CV; in the same group a significantly worse clinical status--scored on the basis of response to treatment--was pointed out. Therefore, a high CV of PEFR may be assumed as a reliable indicator of the risk of exacerbation--not otherwise predictable--both in a short and a longer term; on this basis home monitoring of PEFR may be recommended as a useful tool in the evaluation of all the cases of asthma in remission.