Application of the Ladd fiberoptic sensor to the anterior fontanel of the human newborn has been used as a method for monitoring intracranial pressure noninvasively. This study measures the effect of varying the force with which the sensor is applied to the fontanel. The Ladd sensor readings of five preterm human infants were continuously monitored while sensor application force was increased in a stepwise manner. The Ladd sensor readings for each infant varied with the force applied. In one infant sensor application was gradually increased while direct measurements of lumbar CSF pressure were made. Ladd sensor readings in this infant increased with increasing application force, while lumbar CSF pressure remained unchanged. It is concluded that readings obtained with the Ladd sensor applied to the anterior fontanel of the human infant depend on the force with which the sensor is applied. The effect of application force must be taken into account if noninvasive measurements of intracranial pressure are to be made with the Ladd device.