The study was performed to compare the bioavailability of two gabapentin 400 mg capsule formulation (Gabapentin from Arrow Farmacêutica S/A as test formulation and Neurontin ® from Pfizer, Brazil, as reference formulation) in 26 volunteers of both sexes. The study was conducted open with randomized two period crossover design and a one week wash out period. Plasma samples were obtained over a 48 hour interval. The gabapentin was analyzed by LC/MS/MS, in the presence of pracetamole as internal standard. With plasma concentration vs. time curves, data obtained from this metabolite, the following pharmacokinetics parameters were obtained: AUC 0-t , AUC 0-inf and C max . Geometric mean of gabapentin/Neurontin ® 400 mg individual percent ratio was 100.58% AUC 0-t , 101.35% for AUC 0-inf and 97.76% for C max . The 90% confidence intervals were 92.00 – 109.95%, 93.00 – 110.44%, 88.41 – 108.10%, respectively. Since the 90% confidence intervals for C max , AUC 0-t and AUC 0 -inf were within the 80 – 125% interval proposed by Food and Drug Administration, it was concluded that gabapentin 400 mg capsule was bioequivalent to Neurontin ® 400 mg capsule according to both the rate and extent of absorption.