The potential for gibberellins (GAs) to control stem elongation and itsplasticity (range of phenotypic expression) was investigated inStellaria longipes grown in long warm days. Gibberellinmetabolism and sensitivity was compared between a slow-growing alpine dwarfwithlow stem elongation plasticity and a rapidly elongating, highly plastic prairieecotype. Both ecotypes elongated in response to exogenous GA1,GA4 or GA9, but surprisingly, the alpine dwarf wasrelatively unresponsive to GA3. Endogenous GA1,GA3, GA4, GA5, GA8, GA9and GA20 were identified and quantified in stem tissue harvested atcommencement, middle and end of the period of most rapid elongation. Theconcentration of GAs which might be expected to promote shoot elongation washigher during rapid elongation than toward its end for both ecotypes. Whilethere was a trend for certain GAs (GA3, GA4,GA9, GA20) to be higher in stems of the alpine ecotypeduring rapid elongation, that result does not explain the slower growth of thealpine ecotype and the faster growth of the prairie ecotype under a range ofconditions. To determine if the two ecotypes metabolized GA20differently, plants were fed [2H]- or[3H]-GA20. The metabolic products identified included[2H2]-GA1, -GA8, -GA29,-GA60, -3-epi-GA1, GA118(-1-epi-GA60) and -GA77. The concentration of[2H2]-GA1 also did not differ between the twoecotypes and metabolism of [2H2]- or[3H]-GA20 was also similar. In the same experiments thepresence of epi-GA1, GA29, GA60,GA118 and GA77 was indicated, suggesting that these GAsmay also occur naturally in S. longipes, in addition tothose described above. Collectively, these results suggest that while stemelongation within ecotypes is likely regulated by GAs, differences in GAcontent, sensitivity to GAs (GA3 excepted), or GA metabolism areunlikely to be the controlling factor in determining the differences seen ingrowth rate between the two ecotypes under the controlled environmentconditionsof this study. Nevertheless, further study is warranted especially underconditions where environmental factors may favour a GA:ethylene interaction.