Delineation of downstream signal transduction pathways is important for determining which intracellular signals contribute to the malignant phenotype of cancer cells. In this review, we discuss current methodologies used to study cell signaling. A number of factors that may influence the specificity of signaling will also be taken into consideration. Furthermore, because the HER-2 receptor is amplified and overexpressed in ovarian cancers, we refer to this receptor and its downstream signaling pathways as model systems throughout this review.