Targeted photodynamic therapy (PDT) offers the opportunity of enhancing photodynamic efficiency by directly targeting diseased cells and tissues. While antibody-conjugates have received the most attention, cellular transformations offer numerous other potent targets to exploit during the delivery of photosensitizers (PSs) for PDT. Alterations in receptor expression, increased levels of specific cell surface membrane lipids and proteins as well as changes in the cellular microenvironment all occur in diseased cells. Along with other biochemical and physiological changes that occur during diseased and malignant cell transformation, these factors have been utilized in order to improve the efficacy of PDT. Attempts have been made to either increase the uptake of the dye by the target cells and tissues or to improve subcellular localization so as to deliver the dye to photosensitive sites within the cells. This review discusses various PS bioconjugates that utilize these factors and summarizes the results obtained to date.