Hemocytes are the main immunologic parameters for invertebrate organisms as a response to diseases and pollutions. This study was aimed to reveal the relations between pollution and the total and differential hemocytes numbers. The gulf of Izmir was selected as location for sampling due to its contaminated by different anthropogenic pollutants mainly industrial effects. The effects of the pollutants were investigated on the mussels that have been collected from eight stations in the Izmir Bay (1- Inciralti, 2- Goztepe 3-Konak-4- Pasaport 5-Alsancak, 6-Karsiyaka, 7-Bostanli), which are known as the most polluted part of inner Bay of Izmir (Western Coast of Turkey) and 8-Foca, (an anthropogenically industrialized and shipping -impacted area). The pollution effects in the bay were determined on hemolymphs by biomarkers such as total hemocyte counts (THCs) and differential hemocyte counts (DHCs).