The reactivity of skin blood flow was studied in healthy preterm and fullterm infants, as well as in <1 yr, 5 yr and 10 yr old children and 20 yr old adolescents with or without atopic eczema, using external periodic thermal stimulation. Heart rate (HR), respiratory waveform (resp) and skin blood flow (SBF) signals were recorded using non-invasive methods and further analysed by spectral analysis. Synchronizition of HR and SBF to the stimulus frequency was seen in all studied age groups. The response to external stimulation on HR seems to decrease with maturation and appears to be different in atopic subjects.