We investigated the effect of oxidative stress on the expression of adrenomedullin (AM) mRNA in cultured rat vascular smooth muscle cells (VSMCs), using diethyldithiocarbamate (DDC), which is known to inhibit endogenous Cu, Zn superoxide dismutase (SOD) and to increase superoxide (O₂^-). DDC (10mM) increased O₂^- levels produced from rat VSMCs in a time-dependent fashion. Concomitantly, DDC increased the expression of AM mRNA for up to 24h, although it did not affect the expression of β-ctin mRNA. Thus, oxidative stress enhanced AM production in rat VSMCs, which may compensate for oxidative-stress-induced vasoconstriction. (Hypertens Res 1998; 21: 187-191)