In vivo leaf characteristics were examined to describe longitudinal gradients of UV-absorbing screening pigments in barley. Chlorophyll fluorescence properties and in vivo absorption spectra (210-750 nm) of leaves were measured from the base to the tip. Barley leaves showed strong longitudinal gradients of chlorophyll, where chlorophyll concentration increased within the first 5-8 cm from the leaf base, and did not significantly change for the remaining part of the leaf. Fluorescence microscopy was used to localize cell wall bound screening pigments different from flavonoids, since flavonoids lack a blue-green fluorescence emission (Lichtenthaler and Schweiger 1998). Measurements of in vivo chlorophyll fluorescence indicated that the ratio of UV-absorbing screening pigments per leaf area increases from the leaf base to the tip. These gradients were confirmed by in vivo absorption spectra. It is demonstrated that leaves in the early stage of development are less protected against UV-radiation than fully developed mature leaf regions. The experiments show that measurements of in vivo chlorophyll fluorescence are ideally suited as a fast non-invasive tool to estimate the epidermal UV-transmittance in different leaf sections.