Twenty-one full-term neonates who had a diagnosis of bacterial colonization were randomly assigned to receive amoxicillin 40 mg.kg-1 every 12 hours by either IV or oral route. Plasma levels of amoxicillin were assayed by HPLC at 0.5 (H0.5), 2 (H2), 6 (H6), 9 (H9) hours after the amoxicillin dose for both administration routes and also at the end of the infusion for the IV route. Average levels of plasma amoxicillin with IV and oral routes were not different except at H0.5 where they were higher with the IV route. With oral route Cmax was measured at H2 (6 times) or H6 (4 times). At the end of the infusion, plasma levels were between 55 and 154 mg.l-1 (81 +/- 32 mg.l-1). They decreased quickly so half life of amoxicillin by IV route was between 1.79 and 8.9 hs (4.28 +/- 2.4 hs). They were always above MIC for germs encountered in neonates except at H9 twice with IV and once with oral route. Pharmacokinetic data of this study allow to use oral route for amoxicillin for bacterial colonization in neonates: this administration route could also be proposed in infections following IV route as soon as hemodynamic and gastrointestinal conditions permit. The efficacy of such an attitude could be evaluated by a clinical trial.