AbstractThe effect of vapours from asphaltic bitumen on plants. Asphaltic bitumen vapours escape from hot‐mix asphalt plants and are deposited on leaves and shoots. Experiments were initiated to show whether such droplets cause injuries to plants. Results show that only certain sensitive plants develop symptoms, and then only when more than 3 mg of condensate are deposited per 100 cm2of leaf surface. Injuries caused by bitumen vapours and those caused by coal‐tar vapours were closely related. They were both activated by UV‐light and the symptoms were similar though milder in the case of bitumen. The differences are mainly due to the widely dissimilar content of aromatic hydrocarbons, the photoactivated agents common to the pro