Drawing upon our experience with 88 cases and a survey of the English literature, we reviewed the clinical, pathophysiological, and epidemiological aspects of tularemia. Tularemia can be thought of as two syndromes--ulceroglandular and typhoidal. This dichotomy simplifies earlier nomenclature and emphasizes the obscure typhoidal presentation. Clinical manifestations suggest that the two syndromes reflect differences in host response. In ulceroglandular tularemia the pathogen appears to be well contained by a vigorous inflammatory reaction. Pneumonia is less common and the patient's prognosis is good. In typhoidal disease there are few localizing signs; pneumonia is more common; and the mortality without therapy is much higher, suggesting that the host response is somehow deficient. Francisella tularensis is an extremely virulent pathogen capable of initiating infection with as few as 10 organisms inoculated subcutaneously. During an incubation period of 3 to 6 days the host responds first with polymorphonuclear leukocytes and then macrophages. Granulocytes are unable to kill the pathogen without opsonizing antibody leaving cellular immunity to play the major role in host defense. One to 2 weeks after infection, a vigorous T-lymphocyte response can be detected in vitro with lymphocyte blast transformation assays and in vivo with an intradermal skin test, which, unfortunately, is not commercially available. Humoral immunity, often used as a diagnostic modality, appears 2 to 3 weeks into the illness. Cellular immunity is long-lasting, accounting for the common reoccurrence of localized disease upon repeated exposures to the pathogen. There are no symptoms that distinguish the ulceroglandular from the typhoidal syndrome. A pulse-temperature dissociation is seen in less than half of the patients. The location of ulcers and enlarged lymph nodes give a clue to the likely vector since lesions located on the upper extremities are more commonly associated with mammalian, and those of the head and neck and lower extremities with arthropod, vectors. Pharyngitis, pericarditis, and pneumonia can complicate both syndromes, although the latter is much more common in typhoidal disease. Hepatitis, usually of a mild degree, is common and occasionally erythema nodosum is seen. No specific laboratory tests characterize tularemia, and cultures of the pathogen are often difficult to obtain because of the special growth requirements of Francisella tularesis and the inability of many clinical laboratories to handle the dangerous pathogen.(ABSTRACT TRUNCATED AT 400 WORDS)