Douglas fir needles stained with the fluorescent dye, primulin, were observed microscopically using epiillumination with a mercury arc light source. Microorganisms fell into three categories: algae, which exhibited primary fluorescence; actinomycetes and fungi, which exhibited the secondary fluorescence of the adsorbed dye; and darkly pigmented fungi, which appeared black on the background of the fluorescing Douglas fir needle. A scanning electron micrograph is included for the purposes of comparison.