The endogenous gibberellins of hazel seeds have been studied by a thin layer chromatography/pea epicotyl bioassay (TLC/bioassay) procedure and also by gas-liquid chromatography (GLC) of the gibberellin methyl esters and the trimethylsilyl ethers of the methyl esters. Consistent results were obtained from the two techniques and provisional identifications of some of the gibberellins were obtained by GLC. The gibberellin which was present in the newly harvested seeds, which do not show embryo dormancy, had largely disappeared after the development of embryo dormancy. During 28 days chilling at 5° there was a small increase in endogenous gibberellin but on transfer to 20° there was a considerable rise in endogenous gibberellins, variously estimated as 64-fold (GLC) or 79-fold (TLC/bioassay), this rise preceding the detection of measurable growth of the embryonic axis. The GLC procedure gave provisional identifications of GA1, GA4 and/or GA7, GA5 and/or GA20, GA6 and/or GA17, and GA8. The gibberellin concentration in the embryonic axis was several hundred-fold greater than that in the cotyledons.