Ladd and Wright fontanelle pressure meters were applied to the heads of 18 babies, and simultaneously the intracranial pressure was monitored directly. Increasing the force with which the meters were applied caused a linear increase in registered fontanelle pressure. No universally optimal application force could be determined. To obviate this, application force was increased until the fontanelle pressure was calibrated with directly measured intracranial pressure. Subsequent variations in intracranial pressure were significantly correlated to fontanelle pressure, but not closely enough for clinical reliability. The correlation was similar if the meter was affixed instead directly to the scalp with collodion gel, and the clinical reliability improved. Applanation fontanometers are strongly affected by variations in the method by which they are applied and may not be a reliable reflection of intracranial pressure. If directly affixed to the scalp, however, they may yield clinically useful data.