This chapter examines the aspects of using ELISA to solve problems, definitions of terms met in serology, antibody structure and the production of antibodies in animals, units, dilutions, and molarities. Antibodies—A Laboratory Manual (1) is an excellent manual of techniques relevant to ELISA and all scientists involved in experimental work involving antibodies should have this manual. The manuals given in refs. 2 and 3 also provide extensive relevant practical information.