A severe dwarf mutant affecting vegetative and reproductive growth arose spontaneously in our sunflower-breeding nursery in 1999. The segregation data did not deviate significantly from the expected ratio for a recessive monogenic character. Periodic treatment with gibberellic acid (GA3) was effective to revert to the wild type phenotype and internode elongation was directly related to the GA3 concentration. The results suggest that the mutant gene is involved in the enzymatic pathway of GA synthesis.