We studied the effects of 2, 3, 5-triiodobenzoic acid (TIBA) on berry ripening of 'Kyoho' grapes (Vitis vinifera L.×V. labrusca L.). Compared with the untreated control, application of 200 mg·liter^-1 TIBA 30 days after full bloom (DAF) reduced berry weight and delayed ripening, increased the titratable acidity in the berry, and decreased the anthocyanin content in the peel. TIBA applied 45 DAF, at the beginning of veraison, resulted in higher soluble solids concentration (SSC) in the juice and a higher anthocyanin content in the peel, compared with the control. In a dosage experiment, grape clusters, sprayed with TIBA at 200 mg·liter^-1, had higher SSC and anthocyanin levels than those than sprayed with 20 or 400 mg·liter^-1. The auxin naphthaleneacetic acid (NAA) clearly delayed berry ripening. Abscisic acid (ABA) enhanced peel coloration, but the SSC was equal to that of the control at harvest. When the effects of the antiauxins : N-(1-naphthyl) phthalamic acid (NPA) and maleic hydrazide (MH) were compared with those of TIBA on gibberellin-induced seedless berries, NPA-and MH-treated berries had lower SSC and higher acidity but no effect on peel coloration. TIBA-treated berries had a significantly higher anthocyanin content and SSC than did those of the control. Thus, TIBA application at the beginning of veraison promotes the ripening of seeded and seedless 'Kyoho' grapes.