SUMMARYSix isomers, isolated from the mixture of dinitrophenols obtained by the hydrolysis of commercial formulations containing dinocap, were tested in the greenhouse against apple mildew caused byPodosphaera leucotricha.The two most active compounds were 4‐(Ié‐ethylhexyl)‐ and 4‐(Ié‐propylpentyl)‐2,6‐dinitrophenols, which appear to account for most of the antimildew activity of the mixture. The crotonate of the latter phenol was considerably more effective than dinocap itself, but both crotonates were less effective than the corresponding free phenols.Little evidence of synergism between two ethylhexyldinitropheno