The relevance of age on serotonergic involvement in the control of alimentary contractility has not been pharmacologically described. Experiments were performed to investigate the effects of acetylcholine, atropine, 5-hydroxytryptamine (5-HT) and its related drugs on intestinal segments taken from the neonatal and adult ileum. 5-HT induced concentration-dependent contractions of ileum irrespective of age; however, these contractions were diminished by pretreatment with atropine only in neonatal tissues. In tissues taken from both the neonatal and adult ileum, methysergide (5-HT 1/2/5-7 receptor antagonist), ritanserin (5-HT 2 receptor antagonist), and RS23597-190/SB204070 (5-HT 4 receptor antagonists) all differentially reduced 5-HT-induced contractions at a concentration <100 μmol/l. At higher concentrations, the contractions were comparable to those in control tissues. Granisetron and ondansetron (5-HT 3 receptor antagonists) significantly reduced contractions induced by 5-HT at concentrations >30 μmol/l in both neonatal and adult ileum. Combined treatments with ritanserin, granisetron, plus RS23597-190 reduced or abolished contraction responses induced in neonatal ileum by 5-HT. SB269970A (5-HT 7 receptor antagonist) and WAY100635 (5-HT 1A receptor antagonist) failed to influence contractile responses induced by 5-HT or 5-HT receptor agonists. Pretreatments with WAY100635 and SB267790A also had no influence on the contractile responses induced by 5-HT 1A/7 receptor agonist, 5-CT, and 5-HT 1A receptor agonist, 8-OH-DPAT, which itself failed to induce a measurable response. It is concluded that the 5-HT-induced contractions in segments taken from both the neonatal and adult rat ileum were mediated via 5-HT 2 receptors, 5-HT 3 receptors and 5-HT 4 receptors. However, the effect of atropine on the neonatal rat intestine indicates that the mechanism of serotonergic involvement in ileal contractility is influenced by age.