Microsporidia Encephalitozoon cuniculi, obligate intracellular spore – forming protozoan parasite infecting a wide range of vertebrate and invertebrate host, has been described as opportunistic pathogen in severely immunocompromised human host. An antibody immune response to the presence of antibodies against Encephalitozoon cuniculi was investigated serologically using indirect immunofluorescence antibody test (IFAT). Of the total number of 113 sera from immunologicaly compromised patients examined, 5 were positive at the titre 1:32, 5 at the titre 1:64, and 6 at the titre 1:256. From total number of positive respondent patients were 12 children and 4 adults.

        Key words: microsporidia – Encephalitozoon cuniculi – immunodeficient patients – IFAT.