The 1 fl r n of lants as excited by UV-lasers has r e ! ! o s e c f as a possibility to remotely sense stress effects in terrestrial plants. This blue fluorescence with a maximum near 440, has nothing to do with the red chlorophyll fluorescence. Several secondary plant products such as chlorogenic acid, trans-stilbenes, sinapic acid and possibly other phenolics of the epidermis la er are candidates for emitting blue fluorescence. ðer the blue fluorescence is increased or decreased by stress has yet to be determined as must the nature and composition of blue fluorescing substances in different lant species. The chl r h 11-fl resc nce is characterized gy two maxima .ea?% ind E O A, respectively. The ratio of the two maxima F690/F730 is mainly determined by the chloro hyll concentration of the leaf and to a lower degree also l ! y the photosynthetic activity of plants. The increase of the fluorescence ratio F690/F730 due to shortterm or long-term stress to vegetation is obtained with red or blue laser-light excitation of the chlorophyll fluorescence. The chlorophyll fluorescence ratio F690/F730 is therefore a very suitable parameter for the laser-induced remote sensing of the state of health of terrestrial vegetation.