Giardia lamblia is one of the most common causative agent of gastrointestinal disease in Pakistan and other developing countries with low socio economic indicator, poor sanitation , contaminated water supply and low standards of hygiene which are highly prevalent . The book which is based on Dissertation submitted in Karachi, University of Karachi in 1999 involves the study on 1000 patients with gastrointestinal problems. It gives an insight of the pattern of G.lamblia infection, detection of Giardia or its antigen by different methods, role of immune response and efficacy of different drugs used for patients. The book will be of immense value for researchers, scientists, doctors, paramedical personnel and zoologist. It will also be useful for general public and research students to give an insight of a very common disease of the developing countries.