1. The reaction of the EEG to hyperventilation is discussed with relation to blood sugar levels, to age and to diagnosis. A group of psychoneurotics is described showing an unusual lability of the EEG to hyperventilation in the presence of normal blood sugar values.2. The relationship between the presence of nervous complaints in the early morning and the development of delta activity on hyperventilation in the fasting state was studied. Delta activity develops more frequently in subjects having such complaints than in subjects without them.3. Patients developing delta activity on hyperventilation in the fasting state feel, in a larger percentage, better at later hours than patients without delta activity.4. Two cases of spontaneous hypoglycemia with electroencephalographic studies are reported.