The diagnosis of viral infections is important for the accurate management of patients with infectious diseases and for the monitoring of the course of epidemics in susceptible populations. The utility of traditional viral diagnostic assays is limited by the time, expense, and expertise required for the performance of tissue culture techniques. Similarly, the application of immunoassay techniques has been inhibited by the limited degrees of sensitivity and specificity which can be attained by most immunoassay methods. Recently, techniques for the identification of DNA and RNA have been applied to the detection of viral nucleic acids in clinical samples. Such assays have a number of potential advantages over corresponding immunoassays directed at the detection of viral antigens. In order to be generally applicable to clinical diagnosis, however, formats for the detection of viral nucleic acids have to be devised which allow for the reproducible quantitation of target DNA or RNA in human body fluids. Furthermore, formats need to be devised which allow enhanced assay sensitivity while maintaining high degrees of specificity and reproducibility. The use of non-isotopic labeling, liquid-phase hybridization, and target amplification techniques offers partial solutions to these problems. The development of practical assays for the detection of viral nucleic acids under a broad range of clinical and laboratory conditions would represent a major advance in the ability of physicians to care for patients with suspected infections.