Effects of plant growth regulators on the growth of rhizomes developed from defoliated pseudobulbs of Cymbidium Elfs Castle 'China Peak', as well as ethylene evolution and gibberellin activities in rhizomes were investigated for the utilization of rhizomes for propagation. Rhizomes, growing in the dark, were sprayed with a solution of 100 ppm aminoethoxyvinylglycine (AVG), uniconazole or 10 ppm gibberellic acid (GA3), while the control rhizomes were treated with water and cultured in the dark. A group of water-treated rhizomes were exposed to light (60% of natural daylight). Light-treated rhizomes ceased to grow and but promoted leaf development. AVG decreased the number of nodes and length of internodes of rhizomes, but increased leaf length and number of roots. GA3 promoted leaf growth but did not affect rhizome growth and rooting. Uniconazole reduced rhizome growth without affecting number of nodes and leaf growth, while it promoted rooting. The above treatments were conducted with Cym. 'Miss Taipei' to determine ethylene evolution and gibberellin (GA) substance content. Ethylene evolution from rhizomes 'Miss Taipei' was inhibited by light, AVG, and uniconazole treatments. Bioassays of the control rhizomes revealed that GA3-, GA4- and GA7-like substances were found in fraction numbers of 6, 13, 10 on the TLC plates. GA3-like substance increased in the light-treated rhizomes, but decreased significantly in the uniconazole treatment, whereas AVG had no effect on the total GA-like substance contents. Thus, it is suggested that growth characteristics of rhizomes in cymbidium plants may be controlled not only by GA activities but also by ethylene, and that it is possible to propagate mother stocks by controlling the levels of plant hormones in rhizomes.