Abstract Ascorbic acid effect on sex expression in Cucumis sativus L. – Ascorbic acid affects the sexual gradient of flowers of Cucumis sativus L.; it induces a remarkable production of male flowers (sometimes increases the number of male flowers for each female flower, in respect of control). Indoleacetic acid, instead, induces a femaleness, particularly by reducing the number of male flowers. The maleness induced by ascorbic acid, the earlier the treatment were performed, was the more evident. In groups of plants treated contemporaneously with ascorbic acid and indoleacetic acid, ascorbic acid could prevent the female effect of indoleacetic acid, particularly increasing the number of male flowers produced (almost three times) and of male flowers for each female flower. Also in determining the sexual gradient of flowers of Cucumis sativus L. ascorbic acid shows an action opposite to that of auxin.