AbstractFor maximal color contrast with the dark green copper salt formed in the Uzman reaction, a light red counterstain is required. Nuclear fast red, which stains nuclei light red and cytoplasm a faint pink, gives excellent color and tonal contrasts. This results in high visibility of copper salts and delicately stained tissues, allowing the viewer both to identify tissues and to appreciate the location of the copper deposits. Nuclear fast red, eosin, methylene blue, metanil yellow, picric acid and Harris' hematoxylin were evaluated as counterstains. Nuclear fast red was the counterstain of choice for visual observation, color photomicrography and monochrome photomicrography. Counterstains of eosin and methylene blue were adequate; metanil yellow and picric acid were barely adequate. Hematoxylin and no counterstain were unacceptable for monochrome photomicrography. Nuclear fast red counterstained Uzman sections required a Wratten #11, #59 or #58 filter in monochrome photomicrography, the exact filter depending on the density of the counterstain. Lightly nuclear fast red counterstained tissues required the use of a #58 filter, the more densely counterstained sections, a #59 or #11 filter.