A sunflower (Helianthus annuus L.) mutant was observed in the progeny of a cross between the sunflower cultivar ‘HA 89’ and an amphiploid of a Helianthus divaricatus L. × P21 cross that exhibited loss of dormancy induction in the developing embryo. Seeds of this mutant frequently germinate on the head about 40 days after pollination. The cotyledons of this mutant remain green, whereas some other non-dormant mutants exhibit loss of pigmentation. The objectives of this investigation were to compare levels and activities of abscisic acid (ABA), a plant hormone that induces dormancy in developing embryos, in the non-dormant green mutant (NDG) and ‘HA 89’ from which NDG was derived. Immunoassays showed that abscisic acid was present in NDG and the levels were not significantly different from those in ‘HA 89’. Exposure of excised NDG mutant embryos to 40 μm abscisic acid failed to prevent germination, suggesting that non-dormancy could result from impairment in ABA receptors or from a defect in other proteins participating in the subsequent signalling pathway that normally induces dormancy.