Sheep's cheese is one of the most liked cheese kinds in Turkey. One of the main problems in the manufacture of sheep's cheese is the adulteration of milk with cow's milk, because sheep's milk is more expensive. The aim of this paper was to detect the presence of cow's milk in sheep's cheeses which are sold in retail markets of Istanbul. For this purpose, a total of 100 sheep's cheese samples were purchased randomly from different markets. Immunochromatographic test kit was used to detect the presence of cow's milk in sheep's cheeses. While no adulteration was found in 52% of cheese samples, cow's milk was detected in 48% of cheese samples. These results were considered to be unacceptable. It was therefore concluded that, routine controls on sheep's cheese adulterations have to be performed in Turkey. (c) 2005 Elsevier Ltd. All rights reserved.