Breathing expired gases from bedding .

lation cannot arise. We welcome the authors' recommendation that growth problems be identified at an early age in a community height screening programme. Once screening has been carried out on initial height however, there is little to be gained from waiting a year and screening on velocity using the 25th centile as a cut off, as in the Oxford study. First, the normal short child, on the third centile for height, only requires an average velocity on the 25th centile for steady growth, and single estimates of velocity will fluctuate around this point, with as many below as above. It has been shown that while the proportion of short children growing below the 25th centile remains constant from year to year, the identity of the children inevitably changes.3 The imprecision of the height measurement itself is such that it is rarely possible to label a child's rate of growth, after only one year, as good or poor. A child who is very short must already have sustained a considerable period of slow growth any further delay is therefore