Endogenous indoleacetic acid (IAA) levels were examined in 7-day-old, dark-grown tomato seedlings (Lycopersicon esculentum Mill. cv VFN8), and in two single-gene mutants, Epinastic and diageotropica. Gas chromatography-mass spectrometry was employed to quantify IAA using (13)C(6)-[benzene ring]indoleacetic acid as internal standard. IAA concentrations ranged from 89 to 134 nanograms per gram dry weight and were not significantly different for the three genotypes. Ethylene over-production by dark-grown Epi seedlings is not likely to result from increased IAA. Assuming similar recovery percentages for each genotype, indole-3-ethanol, a purported storage form of IAA, was identified by GC-MS and found to be more prevalent in the parent tomato, VFN8, with only trace amounts observed in Epi. No IEt was detected by high performance liquid chromatography/fluorescence in dgt (detection limit >100 picograms).