Limitations on the use of animals for biological experiments has forced a search for alternative simpler organisms for testing the biological activity of organic com­pounds. The aim of this research was to use Tetrahymena termophila for testing the opioid activity of pep­tide, -casomorphin-7, isolated from cheese. Three kinds of test were used: 1) test for in­hi­bition of protozoa mobility, 2) trap test, and 3) phagocytose test. The results for the trap test suggests that it can be used to determine the presence of harmful substances occurring in food. Determination of the opioid properties using the phagocytose test showed that morphine inhibits the phagocytose process of Tetrahymena termophila. -casomorphin-7 had smaller inhibitory effect on ph­ago­cy­to­sis than mor­phine. it can be said that our results and literature prove the possibility of using protozoa Tet­rahy­mena termophila for studies of antinutritional sub­stances and opioids in raw and food products.