Abstract Spruce needle cinnamyl alcohol dehydrogenase (CAD) was induced in seedlings and four-year-old trees two-to-four-fold by ozone concentrations that did not lead to visible damage. CAD thus acted as an early biochemical ozone marker. A highly purified CAD preparation consisting of two ∼42 000 M r subunits was prepared from spruce cell cultures. A polyclonal antibody was strongly inhibitory. The enzyme had high specificity for coniferyl alcohol and NADP +, and was also detected in spruce seedlings and spruce cambial sap.