After an excellent review of current thinking on adult manic-depressive illness, the authors examine the problems of its nature and the recognition of it in childhood, especially early childhood. It is their speculation that manic-depressive illness may have a quite specific behavioral equivalent in childhood which is infrequently recognized. The fact that it fails to meet many of the adult criteria obscures accurate diagnosis, fails to take into account the impact of affective instability in the developmental process, and results in delayed effective treatment with lithium. Postulating that manic-depressive patients have genetically determined vulnerability of affective systems and supporting their view with a detailed case presentation, the authors state that 'rapidly shifting emotional states in children, which do not seem appropriate to the reality stress, should be carefully evaluated as the possible manifestation of a bipolar affective illness, especially if these states tend to remain prolonged and refractive to therapeutic contact'.