Eight rapid-cyclingBrassicagenotypes differing in height were treated with gibberellins (GAs) by syringe application to the shoot tip. The height of two genotypes ofBrassica napus, Bn5-2 and Bn5-8, andB. rapamutants,dwarf 1 (dwf1)anddwarf 2 (dwf2), was unaffected by exogenous GA3at dosages up to 0.1 μg/plant, a level which increased shoot elongation of normal genotypes. Thus, these dwarf mutants are “GA-insensitive.” In contrast to theB. napusdwarfs, twoB. rapamutants,rosette (ros), anddormant (dor), elongated following GA3application. The dwarfroswas most sensitive, responding to applications as low as 1 ng GA3/plant. Furthermore,rosalso responded to GA1and some of its precursors with decreasing efficacy: GA3>ent-kaurenoic acid ≥GA1>GA20≥GA19=GA44≥GA53. Endogenous GAs were measured by gas chromatography-selected ion monitoring using [2H2]GA internal standards for calibration, from shoots of the GA-insensitive genotypes Bn5-2, Bn5-8 which contained theB. napusmutantdwarf 1, and from a normal genotype Bn5-1. Concentrations of GA1and GA20averaged 3.2- and 4.6-fold higher, respectively, and GA19levels also tended to be higher in the dwarfs than in the norma