Succinic dehydrogenase (SDH) was localized in the mitochondria of Sarcoma 37 ascites tumor cells by the use of tetranitro-BT (TNBT) and nitro-BT (NBT) in smear preparations. Results with each tetrazolium salt as electron acceptor were evaluated with respect to: (a) size and shape of the formazan precipitate relative to standard mitochondrial morphology; (b) crystallization phenomena of reduced dye; (c) lipid adsorption of formazan. The association of formazan- or iron hematoxylin-stained mitochondria with lipid droplets within the cells was investigated, as was also the influence of formalin fixation, with and without cold acetone pretreatment, on mitochondrial morphology and enzymatic staining. Data from these studies appear to indicate that TNBT is more suitable than NBT for use as a cytochemical reagent in oxidative and/or dehydrogenase enzyme histochemistry and cytochemistry.

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