In Arabidopsis thaliana 37 independent irradiation or EMS induced mutants were isolated which have an absolute or almost absolute gibberellin (GA) requirement for germination and successive elongation growth. These are called 'non-germinating GA-dwarfs', since without further addition of GA they develop into typical GA-dwarfs, being dark green, stunted and sterile. However, with repeated GA-treatment they develop into fertile plants with a completely wild type phenotype, or nearly so. In addition, 19 independently induced 'germinating GA-dwarfs' were obtained, i.e. mutants which do germinate without GA but develop into typical GA-dwarfs. With repeated GA-treatment these too grow to become completely wild type phenotypes, or nearly so. 'Germinating dwarfs' have been found by previous authors in a number of other plant species. The 'non-germinating dwarfs' form a new class of mutants. The system of non-germinating mutants offers a resolving power unique in higher plants, so that self-detecting rare events like induced revertants or intragenic recombinants can be efficiently screened for.The 56 GA-sensitive mutants represent mutations at 5 loci, located on three of five Arabidopsis chromosomes. At three of the five loci both mutant classes were represented in similar frequency ratio's, whilst at the other two loci only germinating dwarfs were found.