Background and Aims: The aim of this study was to assess the effects of recombinant human brain-derived neurotrophic factor (r-metHuBDNF) and recombinant human neurotrophic factor 3 (r-metHuNT-3) on gastrointestinal motor functions in healthy people and in patients with constipation. Methods: Gastrointestinal and colonic transit was measured by scintigraphy before and after 2 weeks of treatment. Daily diaries documented symptoms over 6 weeks before, during, and after treatment. In a randomized study of healthy subjects, 40 received 100 μ/kg r-metHuBDNF or placebo subcutaneously (SC) daily. In a separate study, 8 healthy subjects and 8 patients with constipation received 300 μ/kg r-metHuNT-3 SC thrice weekly. Results: r-met- HuBDNF accelerated overall and proximal colonic emptying (P < 0.05) in health, r-metHuNT-3 accelerated overall colonic transit in health and constipation (all P < 0.05) and gastric and small bowel transit (both P < 0.05) in health, r-metHuBDNF tended to increase stool frequency compared with placebo in health (P = 0.09). r-metHuNT-3 increased stool frequency (P = 0.05) and facilitated passage of stool (P < 0.01) in constipated patients. The effects on stool frequency started within 3 days of the beginning of neurotrophin administrations and lasted up to 5 days after treatment ended, r-metHu neurotrophic factors were well tolerated, although half of the participants in the 2 studies developed injection site reactions or paresthesiae. Conclusions: Exogenous neurotrophic factors stimulate human gut motility in health and constipation.