In cultured vascular smooth muscle cells, angiotensin II and endothelin stimulate a variety of intracellular signals, including generation of inositol trisphosphate and diacylglycerol, mobilization of intracellular calcium, and activation of protein kinase C. These latter two events have been shown to mediate the phosphorylation of numerous proteins, but these substrates and the specific pathways mediating their phosphorylation have not been identified in vascular smooth muscle. Angiotensin II (100 n M, 10 min) induced a characteristic pattern of protein phosphorylation, which included the phosphorylation of many proteins, ranging in molecular mass from 20 to 76 kD. Three of these proteins have been identified as vimentin (M<sub>r</sub> 57,000), a specific protein kinase C substrate (M<sub>r</sub> 76,000) and the myosin light chain (M<sub>r</sub> 20,000). The 76-kD protein was one of the most highly phosphorylated proteins after agonist treatment. Endothelin-1 produced an identical pattern of phosphorylation. Five of these substrates were also phosphorylated by phorbol-12-myristate-13-acetate, and 5 were also phosphorylated after treatment with ionomycin. In general, the protein-kinase-C-dependent phosphorylations were sustained, while those mediated by calcium were rapid. Since these experiments were performed in cultured, phenotypically modulated cells stimulated with agents that promote cellular hypertrophy or hyperplasia, this pattern of phosphorylation may be representative of that seen during the growth response.