Naturally occurring gibberellin-like substances possessing acidic, basic, and neutral properties were detected, by paper partition chromatography, in ethanolic extracts of tomato seed and of etiolated seedlings after 72 and 116 hours' growth. Dwarf maize mutants of the d-1 and d-5 types, ‘Meteor’ pea seedlings and young ‘Potentate’ tomato plants were used as bioassay material. Hydrolysis of seed and seedling proteins by ficin in phosphate buffer, pH 6.2, after removal of ethanol-soluble substances, liberated more and different ‘bound’ gibberellin-like substances. It is suggested that protein hydrolysis during germination is an important means of liberating these substances at different stages of seedling development. Acidic substances were present in all the extracts prepared, but in general two with Rfs 0.25 and 0.55 in iso-propanol: ammonia: water : : 10:1:1 v/v were differentiated on d-2 and d-5 maize respectively. Neutral substances in dry seed extracts chromatographed in the same solvent, had Rfs of 0.05, 0.35, and 0.95 and these were found only in the ethanolic (‘free’) extracts. They were active on d-1 and d-2 maize and ‘Meteor’ pea. Basic gibberellin-like substances with Rfs of 0.05 and 0.35 were found in ‘free’ extracts of both dry seed and etiolated seedlings after 116 hours' growth which were active on d-2 maize only. Two others with Rfs 0.45 and 0.95 were extracted from seedlings after 72 hours' growth and these were active on young ‘Potentate’ tomato plants. It is suggested that certain gibberellin-like substances, capable of reversing dwarfism in test plants, may be responsible for morphogenetic or other responses not involving stem extension in the parent species. Changes were found in the levels of gibberellin-like substances but there was no evidence of changes in levels of seed inhibitors relative to seed growth substances.