SILKOFF et al. [7] hypothesised that increased Daw,NO might be an early manifestation of asthma. However, we found no evidence to support this, since the distribution of Daw,NO was similar for both groups. In contrast, the range of Caw,NO values in the wheezers appeared to be higher than in controls. In asthmatics, Daw,NO is elevated compared with controls [7, 8] but Caw,NO is not [7]. Factors determining Caw,NO and Daw,NO may be different in infants with early asthma symptoms compared with older individuals who have established disease.Among the control subjects in the present study, values of Daw,NO in controls were higher than reported previously (range 3-37 nL?s -1 ?ppb [4]) and CawNO values were lower (49-385 ppb [4]). Apparent differences in FIP values between studies are most likely explained by the small numbers of participants in both studies. In addition, the FeNO values at low flows, known to predominantly influence Daw, NO and Caw,NO [1] differed between studies. The majority of mothers of control infants in the present study were atopic and this is relavent since maternal atopy is known to influence nitric oxide in infants [9].