In 102 school children aged 7 to 12 yr with diagnosed asthma or wheezing in the past 12 months spirometry was performed three times in 4 to 6 weeks intervals. Maximal expiratory flows at low lung volumes (MEF50 and/or MEF25) were reduced in more than one third of children. The reduction of MEF50 and MEF25 was more frequent, more deep, and more persistent in following tests as compared with FEV1%. Small airways obstruction was observed in almost 90% children with FEV1% slightly above limit value.