Airway remodelling is a structural alteration associated with chronic inflammatory and obstructive airway diseases, wherein fibroblasts are crucially involved. The present study investigates whether lung fibroblast proliferation is influenced by muscarinic mechanisms. For this purpose expression of muscarinic receptors in MRC-5 human lung fibroblasts was characterised by semi-quantitative RT-PCR, and the effects of muscarinic agonists and antagonists on (³H)-thymidine incorporation as a measure of proliferative activity were studied under different culture conditions. MRC-5 fibroblasts express mRNA encoding different subtypes of muscarinic receptors (M₂ > M₃ > M₄, traces for M₅ and no M₁). Expression of M₂ and M₃ receptors was confirmed at protein level by immunoblot analysis. Under different culture conditions, carbachol (up to 10 µM) or oxotremorine (10 µM) stimulated (³H)-thymidine incorporation with maximum increases between about 40% and 100%. The stimulatory effect of 10 µM carbachol was prevented by pre-treatment with pertussis toxin and antagonized in a concentration dependent manner by the muscarinic receptor antagonists tiotropium, AQ-RA 741, AF-DX 384, 4-DAMP, himbacine, p-fluorohexahydrosiladifenidol and pirenzepine with IC₅₀ values of 14 pM, 24, 64, 127, 187, 452 nM and 1.5 µM, respectively. Primary human lung fibroblasts were also found to express mRNA for muscarinic receptors (M₂ > M₁ > M₃, traces for M₄ and no M₅) and showed a pertussis toxin-sensitive proliferative response to muscarinic receptor stimulation. In conclusion, proliferation of human lung fibroblasts can be stimulated by activation of muscarinic receptors with a pharmacological profile correlating best to M₂ receptors.