Excessive vagal tone has been implicated as the cause of pallid breath-holding spells (PBHS) in children. The following study was undertaken to test the hypothesis that children with PBHS have underlying autonomic nervous system (ANS) dysfunction. Five patients (age 29-79 months old) who had experienced PBHS were evaluated at a time when they were clear of spells for ANS dysfunction. A battery of clinical bedside tests were given. The results were compared with test results of a control group of children (age 18-104 months) who had not experienced PBHS. Data collected included blood pressure, pulse rate, mean arterial pressure, the 30:15 R-R ratio upon standing, the expiratory:inspiratory (E:I) R-R ratio, pupillary response to conjunctival pilocarpine instillation, and plasma norepinephrine levels upon standing. Breath-holders displayed a statistically significant (p less than 0.05) percent decrease in mean arterial pressure (-10.2% PBHS vs. -4.1% controls) and an unsustained increase in pulse rate during the lying to standing maneuver. Two children with PBHS had "positive orthostatic signs," and one child with PBHS had a plasma norepinephrine level of 94 pg/ml (60% below the mean for both groups). There is evidence to suggest a subtle, underlying, generalized autonomic dysfunction in children with PBHS. A strong familial tendency toward syncope, breath-holding spells, and seizures was recognized in nine of ten subjects. Additionally, there was a strong influence from the maternal side of the family in seven of nine subjects.