The main problem of serologic examinations is the correct interpretation of serological findings. Essentially, there are two reasons for serologic examination. The first one is simply the need to know if the person examined has antibodies against the agent in question. Here the interpretation of the result is easy. In the second case, the question hidden behind the inquiry if the patient has antibodies or not is entirely different: namely, if the patient is experiencing the infection caused by the agent in question. Since the serologic results do not equate with medical diagnosis, their correct interpretation is difficult, if not impossible. For the diagnostic purposes we must usually examine two specimens of the serum and demonstrate significant changes in the titre of antibodies. Examples are given when it is exceptionally possible to diagnose an infection from the serologic result of the single specimen. Generally, the interpre- tation must take into account: 1. the kind of the infectious agent, 2. the pathogenesis of infection, 3. the course of the immune reaction ascertained by the detection of antibody activity in different classes of immunoglobulins or by the demonstration of low-avidity antibodies, 4. technicalities as the type of serologic reaction, 5. individual reactivity of the patient and, most importantly, 6. time data on the duration of the illness. The attending physician should have adequate knowledge of serologic methods and the laboratory worker should be informed about the disease and about the individual patient in question.

        Key words: serology - interpretation of result - detection of antibodies - titre of antibodies.