Abstract: Adenosine triphosphatase activity in watermelon stigma papilla cells was studied. In cells with active secretion, enzyme reaction product was present in large quantities on the plasma membrane, vacuo le membrane, plasmodesma and in the endoplasmic reticulum, plastid lamellae,and only in small quantities in the mitochondria and small vesicles.In cells which began degeneration and thus stopped secretion, enzyme reaction product was localized mainly on the vacuole membrane. The high adenosine triphosphatase activity on plasma membrane indicated that the transportation of secretion needs plenty of energy, and such enzyme activity in the endoplasmic reticulum may indicate that this organelle system is involved in the synthesis of secretion.