There is accumulating evidence which points to a role of Serotonin (5-hydroxy tryptamine) in the pathophysiology of asthma. Therefore, we analyzed the expression of serotoninergic receptors (5-HTR), its linkage to intracellular calcium homeostasis and its influence on the production and secretion of interleukin (IL)-6, Prostaglandin E₂, the CCL-Chemokine CCL5/Rantes and the CXC-chemokines CXCL8/IL-8, CXCL9/MIG, CXCL10/IP-10, CXCL11/I-TAC in primary alveolar epithelial cells type II and the human lung cell-lines A549 and BEAS-2B. Employing a PCR approach we were able to demonstrate mRNA expression of several 5-HTR such as the heptahelical receptors 5-HTR1A, 5-HTR1B, 5-HTR1E, 5-HTR1F, 5-HTR2A, 5-HTR4, 5-HTR6 and 5-HTR7, as well as the ligand-gated ion channel 5-HTR3 in AECII, A549 and BEAS-2B cells. To verify functional expression of 5-HTR subtypes, Ca²⁺-transients were analyzed. Hereby we could show that 5-HT induced an increase in intracellular calcium. Further experiments with isotype-selective receptor agonists allowed us to demonstrate that 5-HT induced calcium transients via activation of 5-HTR1, 5-HTR2 and 5-HTR3 in A549 and BEAS-2B cells. Moreover, we revealed that stimulation of 5-HTR1 and 5-HTR2 induced Ca²⁺ mobilization from intracellular stores, whereas activation of 5-HTR3 induced Ca²⁺ influx from the extracellular space. Functional studies indicated that activation of 5-HTR1B, 5-HTR1E/F, 5-HTR2, 5-HTR3, 5-HTR4 and 5-HTR7 regulated the release of the cytokine IL-6 and the CXC-chemokine CXCL8/IL-8. Our study shows that 5-HT stimulates different signalling pathways and regulates cytokine release in airway epithelial cells. In summary our data implicates a pathophysiological role of 5-HT in the asthmatic inflammatory responses in human airway epithelial cells.