Recent results from our laboratory include: (1) the discovery of a novel organelle in trypanosomatids that we later identified in Apicomplexan parasites, other unicellular eukaryotes, bacteria, and human platelets that we named the acidocalcisome, because it is acidic and contains a high calcium concentration. This organelle is conserved from bacteria to man; (2) the finding that bisphosphonates, drugs approved for use in humans against osteoporosis and other bone diseases, are effective antiparasitic agents and offer a potential new route to chemotherapy of parasitic diseases; and (3) the discovery that human platelet dense granules possess a high concentration of polyphosphate, being similar to acidocalcisomes, and that polyphosphate is released from platelets after thrombin stimulation and has a physiological role in coagulation and fibrinolysis.