We have examined the inward-rolling and outward-opening of petals from $90^{circ}$ stage carnation flowers (Dianthus charyophyllus L. cv. Pink Donor). Ethylene released from 2-chloroethylphosphonic acid (CEPA) induced in-rolling in the lower portions of the petals while that action was suppressed by an inhibitor of auxin transport. Another plant hormone, indole-3-acetic acid(IAA), intensified this ethylene-induced in-rolling. In contrast, when ethylene was not applied, the same IAA concentration promoted the opening of petal segments. Our data suggest that a low level of ethylene acts on IAA-induced opening. Likewise, we can speculate that endogenous concentrations of ethylene could be an important determinant of petal responses that involve interactions between ethylene and IAA.