The polyamines, spermidine and spermine, and their diamine precursor, putrescine, constitute a unidirectional biosynthetic pathway whose biosynthetic enzymes and accumulation patterns appear to play important roles in the regulation of growth processes. Concentrations of these compounds in physiological fluids are low or undetectable under normal conditions, are elevated in patients with metastatic cancer, and are thought to reflect growth (putrescine concentrations) and cell turnover (spermidine concentrations) of the organism. Cancers are a broad spectrum of diseases in which there are altered growth fractions and cell-turnover fractions, and therefore cancer chemotherapeutic agents have been developed to take tumor kinetics into account. Because changes in polyamines in physiological fluids reflect cell kinetics, this review compiles evidence of their efficacy as biochemical markers of cancer and suggests their possible usefulness to clinicians in rapidly assessing tumor response to chemotherapy or to multimodality therapy.