Various extracellular stimuli activate three classes of mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 MAPK. In mammalian cells, p38 MAPK is activated by endotoxins, inflammatory cytokines, and environmental stresses, We show here that p38 MAPK is also activated upon stimulation of G protein-coupled receptors (G(q)/G(11)-coupled m1 and G(i)-coupled m2 muscarinic acetylcholine and G(s)-coupled beta-adrenergic receptors) in human embryonal kidney 293 cells. The activation of p38 MAPK through the m2 and beta-adrenergic receptors was completely inhibited by coexpression of G alpha(o), whereas the activation by the mi receptor was only partially inhibited. Furthermore, we show that overexpression of G beta gamma or a constitutively activated mutant of G alpha(11), but not G alpha(s) and G alpha(i), can stimulate p38 MAPK. These results suggest that the signal from the m2 and beta-adrenergic receptors to p38 MAPK is mediated by G beta gamma, whereas the signal from the m1 receptor is mediated by both G beta gamma and G alpha(q/11).