Abstract
The intracellular localization of porphyrin taken up by a transplanted rat tumor has been studied. Quantitative determination of the porphyrin concentrations in the subcellular fractions and direct observation by fluorescence microscopy indicate that porphyrin accumulates in the soluble fraction and not in the cell wall, nucleus, mitochondrial, or microsomal particles. There is suggestive evidence that selective uptake by the soluble fraction is due to a specific constituent to which the porphyrin is bound.