The binary mixture of the hydrocarbons (3Z,6Z,9Z)-3,6,9-nonadecatriene and (6Z,9Z)-6,9-nonadecadiene is a sex attractant for males of Alsophila quadripunctata Esp. (Lepidoptera, Geometridae). Triene/ diene ratios from I: 1 to 1:0.01 attracted males in the field, the ratios 1:1 and 1:0.7 were most effective. The triene on its own also attracted males, but in significantly lower numbers than the i: 1 mixture. In a dosage test the highest dose, 1 800 #g of 1:0.8 [triene:diene] mixture applied to rubber caps was most effective. This is the first report of a geometrid sex attractant with field activity containing more than one component.