Parasitic and bacterial infections affecting the gastrointestinal tract represent a significant cause of morbidity and mortality worldwide. Nitroheterocyclic drugs have been available since the early 1960s for the treatment of anaerobic protozoa. The application of these drugs has widened and they are presently used to treat anaerobic pathogenic bacteria and protozoa. 5-nitroimidazoles are a well-established group of antiprotozoal and antibacterial agents that inhibit the growth of both anaerobic bacteria and certain anaerobic protozoa, such as Trichomonas vaginalis, Entamoeba histolytica and Giardia lamblia. The important antibacterial and antiprotozoal activities of nitroimidazoles are associated with reductive metabolism that has led to considerable interest in nitroimidazole reduction chemistry and the synthesis of new, highly effective drugs. The present review provides a brief account of various biological activities exhibited by synthetic nitroimidazole derivatives as well as their structure–mutagenicity relationships.