Lumbar CSF pressure (CSFP) was measured on 61 occasions, in 49 babies undergoing lumbar puncture as part of a septic screen, by means of Gaeltec pressure transducers. In normal circumstances, intracranial pressure (ICP) has the same value. Measurements were made when the baby was horizontal and quiet, with the head deflexed. For acceptance of the measurement, it was essential for the CSF to be clear and to show pressure pulses with respiration, heartbeat and jugular occlusion. The mean CSFP and standard deviation were 2.8 +/- 1.4 mm Hg (3.8 +/- 1.9 cm water), with a normal range of 0 to 5.7 mm Hg (0 to 7.6 cm water). This value is similar to previous reports of CSFP measured invasively in infants, but is much lower than the "ICP" established noninvasively. No relationship was found between birthweight, gestational age, current weight, postmenstrual age, or postnatal age and CSFP.