Opportunistic infections (OI) have gained ing much importance nowadays. A number of parasitic pathogens have emerged causing widespread infections. Several factors affect the patterns of diseases. These include AIDS pandemic, increased immigration, travelling, social habits, etc. On the other hand,intensive research activity has yielded numerous new data about OI causing pathogens in recent years. Protozoas are the predominating pathogens of OI. Many newly identified parasites including coccidian forms, such as Cryptosporidium, Cyclosporaand Isospora, present a challenge for. This review was aimed to give information about the above mentioned parasites, mainly in connection with the intestinal symptoms of OI caused by them. The importance of the topic of emerging OI is related to the situation of HIV in our country. The knowledge of these parasites and their life cycles will contribute to the recognition, treatment, and possible prevention of OI.