Blow flies (Diptera, Calliphoridae) and their medical applications have attracted the attention of biologists and doctors for more than a century. The best known is the use of “surgical maggots” in the treatment of infected wounds and ulcers. Another promising direction is the use of Calliphoridae as producers of pharmacologically active substances. Compounds with antiviral and antitumor activity isolated from blow fly maggots have found application in the treatment of viral infections. The maggot enzymes and antimicrobial peptides are another group of drug candidates that have received much attention. This review summarizes information on Calliphoridae as a source of new drugs and the prospects for their use in solving the urgent problems of modern medicine, such as the growing antibiotic resistance of pathogens, the treatment of viral infections and cancerous diseases.