To evaluate whether L-arginine methyl ester (L-Arg) can improve the structure of the small intestine and enhance adaptation in an experimental model of short-bowel syndrome (SBS), 40 Sprague-Dawley rats were divided randomly into four groups of 10 each. In one group only a laparotomy was performed (G1). The remaining 30 rats underwent 90% small-bowel resection (SBR) and formed the three experimental groups: the SBR/untreated group (G2), the SBR/L-NAME-treated group (G3), and the SBR/ L-Arg-treated group (G4). Rats in G2 received no therapeutic treatment. Rats in the SBR/L-NAME and SBR/L-Arg treated groups received N-G-nitro-L-arginine-methyl ester (L-NAME) and L-Arg intraperitoneally for 3 weeks, respectively. The animals were weighed daily. All rats underwent a relaparotomy on day 21 of the experiment. Remnant small bowel was excised and evaluated for villus height and crypt cell mitoses. After the 90% SBR, all animals had from diarrhea and weight loss between the 1st and 6th postoperative days (POD). The body weight of the SBR/L-Arg group showed significant increases at POD 10 and 21 in comparison to the SBR/untreated and SBR/L-NAME groups (P < 0.001). The rats treated with L-Arg had significantly greater villus height and crypt-cell mitoses compared to the other groups (P < 0.0001, P < 0.001). These observations suggest that L-Arg treatment increases villus height and crypt-cell mitoses after massive SBR and may play a considerable role in the mucosal adaptive response in SBS in rats.