PIP: In this article the authors describe the necessity of being able to test human blood for pathogens and, in particular, HIV. HIV serodiagnostic techniques are then described as follows. Detection of HIV-specific antibodies can be done by using one or more screening procedures. These are the enzyme-linked immunosorbent assay (ELISA) and two tests, generally called the rapid test and the simple test. When using ELISA, the following antigens are used to detect HIV antibodies synthetic peptides, recombinant DNA (protein), and viral lysate. Two important factors used in determining a given test's usefulness are the sensitivity and specificity of a test for the agent in question. The probability that a given test is truly accurate in predicting that the infectious agent is present or not is in large part determined by the HIV prevalence in a given population from which the individual being tested comes. Rapid tests are fast, taking 30 minutes or less to complete, and expensive. They are useful in emergency situations where time is a critical factor in health care treatment. Two types of rapid tests, the latex agglutination assay and the dot blot assay, are briefly described. Simple tests are very similar to rapid tests, except they are not as fast. These take over 30 minutes to complete. They, too, are based on the principles and techniques used in latex agglutination assaying. They are also less expensive. In India, where both HIV-1 and HIV-2 infections may be found, the government supports follow-on supplemental tests to confirm the initial diagnosis for positive HIV. Supplemental assays may confirm a positive finding and provide additional information about the HIV type. Examples of supplemental tests are the Western blot, immunofluorescence assay (IFA), pepti-LAV assay, and virus isolation. Detection of antigen p24 in the serum may also be used in late-illness patients. Other techniques mentioned are: detection of viral nucleic acids by using in situ hybridization with radioactively labeled RNA or proviral DNA; and polymerase chain reaction (PCR), in which suspect RNA or DNA is amplified and plated on gel material. PCR is the most sensitive test for identifying an HIV infection. Skin hypersensitivity test, and select serological tests are incomplete but are being studied.