IT was hypothesized that adult handedness might be predicted from the neonatal grasp reflex. Grasp reflex was measured from right and left hand (10 trials for each hand) in neonates. According to significance for the difference between the mean grasp reflex strength from the right and left hands, the subjects were designated as right-, left-, and mixed-handers. Adult hand preference was assessed by Edinburgh Handedness Inventory. The percentage of left-handedness (8.3%) in neonates coincided with adult left-handedness (6.3-9.2%): The percentage of consistent right-hand preference In adults coincided with percentage of right-handedness in neonates (25.7%). The high percentage of neonatal mixed-handedness was similar to that to be expected from the right shift model of hand preference. It was concluded that left-handedness and consistent right-handedness may be determined prenatally, under genetic and/or hormonal control, and that a large majority of neonatal handedness, mixed-handers, might change their hand preference in favor of right-handedness under socio-cultural and developmental influences of speech centres. NeuroReport 10:3253-3256 (C) 1999 Lippincott Williams & Wilkins.