M.P. Sharma, D.M., and S.K. Acharya, M.D. Giardia, first recognized by Von Leeu- wen hoeok 300years ago in his own stool? remains an enigma as yet. It's pathogenesis in causing disease is com- p'lex and unclear, though manifestation in human beings as asymptomatic cyst passers to frank malabsorption is well known. This brevity of knowledge about the disease process hails from, lack of indentification of true numbers of distinct giardia species, pathogenetic mechanism of the disease and host immunological response. The definition of antigenic differences among parasite species awaits isolation of these antigen. The absence of this immunological technology leaves the immunology of giardiasis at the state of gross pheno- menological description. However, present knowledge of immunological aspects of giardia infection, throws some ~ light to the disease caused by this parasite. Three aspects of giardia infection will be considered,