The clinical immunology laboratory provides support to the allergist in the diagnosis and management of human allergic diseases. Following a clinical history, the detection of allergen-specific immunoglobulin E (IgE) in serum can be useful in the definitive diagnosis of an IgE antibody-mediated hypersensitivity. Total serum IgE, the multiallergen screen, and mast cell tryptase are less commonly measured analytes in the work-up of the allergic patient. More recently, the clinical laboratory has employed monoclonal antibody based-enzyme immunoassays to quantify dust mite, cat, dog, and cockroach indicator aeroallergen levels in indoor home and work environments. Levels of allergenic proteins in environmental and medical/consumer products are measured by other assays such as the competitive inhibition radioallergosorbent test. Methods of quantification, internal quality control, and external proficiency testing programs are emphasized in this report.