The effects of cxogenous hormones (ABA, NAA, BA, GA3, and ethephon) and chemical inhibitors (MH and CIP), associated with cooling, on sprouting of dormant (freshly harvested) and non dormant (kept six months at 5-6 °C) onion bulbs were investigated. Effects of NAA and BA on the sprouting of the bulbs were similar, particularly when associated with cooling. Cooled + NAA and BA treated domant bulbs, both sproutcd after 10 weeks, while non-cooled bulbs sprouted after 10 and 12 weeks, respectively. Non-dormant bulbs sprouted after 3 and 4 weeks, respectively. No significant effect of MH, CIP and STS on sprouting of non dormant bulbs was observed. Gibberellin and ethylene were less effective on sprouting of dormant onion bulbs. Nevertheless significant differences were observed between GA3 or ethylene treated and cooled bulbs, and others treated bulbs. For non dormant bulbs, significant differences were noted among GA3,-ethephon-control, and MH-CIP treated bulbs. Sprouting of bulbs was also affected by ABA treatment, while cooling slowed down significantly this inhibitory effect of ABA.