CD-1 Swiss mice were used to study the effects of repeated intracerebroventricular (i.c.v.) injections, on postnatal days (PND) 3, 6, 9, of rabbit antiserum (50 micrograms) raised against murine nerve growth factor (NGF) both on locomotor activity in an open field test (PND 10) and on a passive avoidance learning test (PND 11 and 12). While no difference was evident in locomotor activity levels between anti-NGF and control pups, an impairment of anti-NGF pups was detectable in the passive avoidance performance. Removal of endogenous NGF seems to produce a detrimental effect on a behavioural performance which is known to be under central cholinergic control, confirming previous reports on the role of NGF in early neurobehavioural responding in altricial rodents.