Smooth muscle is important for the contractility and elasticity of visceral organs. The zebrafish is an excellent model for understanding embryonic development, yet due to a lack of appropriate markers, visceral smooth muscle development remains poorly characterized. Here, we develop markers and trace the development of gut and swim bladder smooth muscle in embryonic and juvenile fish. The first smooth muscle marker we detect in the vicinity of the gut is the myoblast marker nonmuscle myosin heavy chain-b at 50 hours postfertilization (hpf), followed by the early smooth muscle markers SM22␣-b, and ␣-smooth muscle actin at 56 and 60 hpf, respectively. Markers of more differentiated smooth muscle, smoothelin-b and cpi-17, appear by 3 days postfertilization (dpf). Tropomyosin, a relatively late marker, is first expressed at 4 dpf. We find that smooth muscle marker expression in the swim bladder follows the same sequence of marker expression as the gut, but markers have a temporal delay reflecting the later formation of swim bladder smooth muscle. Developmental Dynamics 236:1623-1632, 2007.