The microscopic recognition of Borrelia burgdorferi in biologic fluids and tissues is difficult and challenging because of low numbers of organisms occurring as single isolated spirochetes, the apparent lack of colony formation in tissues, and differing lengths and structural morphologies. To identify the most common morphologic forms, we studied numerous cultures by a variety of microscopic techniques. Culture suspensions of B. burgdorferi were stained by several different histochemical procedures (Gram, Wright, Wright-Giemsa, Giemsa, and polychromes), fluorochromes (thioflavin-T, acridine orange, and rhodamine), silver impregnation techniques (Warthin-Starry, modified Dieterle, modified microwave Dieterle, and Bosma-Steiner) and immunocytochemical methods with different polyclonal and monoclonal antibodies. Additionally, borrelia culture suspensions were embedded in agar and also injected into skin biopsies and processed for histologic study. The different staining properties were found to be influenced by fixation methods and the type of antibody in immunocytochemical stains. This study provides evidence for marked cytomorphic variations in individual spirochetes. Variations detected by these staining procedures provide a basis for future study of tissue sections and for how borreliae can be expected to appear in tissue sections.