The field of clinical immunology is advancing rapidly and will continue to grow and benefit from the knowledge gained in different areas of basic immunology. The diagnosis and evaluation of a child with a suspected primary immune defect can be a challenging task that should be done carefully using the best available laboratory resources. Simple laboratory screening tests, available to most pediatricians, can be done initially and will provide an idea of the level of general immune competence. Referral for a more detailed evaluation should be made in selected cases. A basic understanding of the tests used in immune evaluation, as well as the fact that the results may be affected by multiple variables, is important. Of equal significance is the interaction of the physician with the laboratory in which the samples will be analyzed. Proper sample collection and handling as well as prompt processing by the laboratory are crucial. Equally important is the physician's interpretation of results in the context of the pediatric population. Tests like lymphocyte studies, WBC studies, immunoglobulin subclasses, response to antigenic challenge, and certain complement assays require a higher degree of expertise and should only be sent to laboratories with experience in performing them. Physicians need to gain confidence in the power of diagnosis that the immunology laboratory brings to their patients.