Changes in endogenous levels of IAA, GA and ABA during in vivo fiber growth of Gossypium arboreum L. (cv. LD 327) showed an over-riding influence of ABA in limiting the rate of fibre elongation. The fibre growth of unfertilized cotton ovules cultured in vitro was elevated by the application of fluridone, which markedly decreased the ABA level concomitant with an increase in the levels of growth promoters (IAA, GA₃) in cultured ovules. The enzymatic hydrolysis of b-glucopyranosyl ester of ABA by b-glucosidase and esterase were studied in fibres at 15 and 35 days after anthesis. Since the activity levels of two hydrolases did not correlate with the free ABA contents at two stages of fibre growth, it is suggested that the high content of free ABA at 15 days after anthesis (DAA) was not a consequence of the increased activity of the ABA-Glc splitting enzymes. Our data suggests that ABA conjugate is the final product of the ABA metabolism under different stages of fibre growth.