Electric stimulation was applied to the tooth-pulp and tongue in 12 children divided into 3 groups according to the development of the roots of the upper first incisors, i.e. 1/2, 3/4 and fully formed. The masseter inhibitory periods (MIP) could be evoked by electric stimulation of the tongue at sensory threshold current levels in all children, but only for incisors with fully-formed roots. Stimulation of incisors with 3/4 formed roots at detection-threshold currents produced sensation 56 per cent of the time and detectable MIP on 65 per cent of stimuli. No sensation was obtained with stimuli up to 100 microA in incisors with 1/2-formed roots, but MIP was recorded with 31 per cent of stimuli. The findings indicate that reflex activity precedes sensation in the normal development of teeth, and that segmental, reflex, connections appear to be established before the cortical, sensory, projections are fully functional.