Among the infections; requires consideration of many enteritis: acute Salmonella infection is usually recognizable by blood culture in the first week of illness, and positive serologic test in the second week of starting of fever. Enteric fever, especially Typhoid fever usually have no distinctive clinical and laboratory features and should therefore be considered in all febrile ill-nesses (1) The ineffectiveness of Amoxicillin in this patient however is -evidence against infection with Salmonella infection. Absence of biphasic presentation with an influenza-like illness and conjunctivitis and signs of intera- cranial hyper pressure, the possibility of Leptospirosis is unlikely. Absence of rhythmic rigor and high fever and sweating, the characteristics of Malaria disease makes a weak diagnosis for malaria and probably impossible. Urinary tract infections and acute bacterial endocarditic are probably unusual with this kind of signs and symptoms. In a patient with an involuntary weight loss, and a non-specific febrile illness with a mild leucopenia and lymphocytosis with non specific chest X-Ray findings, and positive PPD mycobacterium infection in the from of extra pulmonary infection is a strong consideration. This patient probably does not have intestinal or genitourinary T.B since in such cases the overall clinical picture tends to reflect the main focus of infection. 2)ln this patient; there's a clinical picture that is very suggestive of Brucellosis, an enzootic disease, The clinical findings are compatible with the acute Brucellosis, a clear blood culture and a bone marrow aspiration culture may be a diagnostic clue for Brucellosis especially in the beginning of disease when standard serologic tests for Brucellosis are still non-reactive. Fever without focal findings are altogether the best diagnosis and in this group of infectious diseases, Brucellosis is an important diagnosis, and it should be keep in mind that in this group of infectious diseases, sandfly disease, endemic Typhus, Q'- Fever, Histioplasmosis, Toxoplasmosis are important too, and all can be in our differential diagnosis but in a second stage. Urosepsis, Vasculitis, EBV infection are other conditions mimicking fever without focal findings .Diagnostic procedure in this case probably is a bone marrow aspiration culture with positive result for Brucellosis. Discussion: Human brucellosis is traditionally described as a disease of protean manifestation (2)- Physical examination is generally none-specific, though lymphadenopathy, hepatomegaly, or splenomegaly is often present. (2-4) the blood count is often characterized by mild leucopenia and relative lymphocytosis, along with mild anemia and thrombocytopenia (2-5-6) and development of the first serologic test for Brucellosis. More than a century ago a definitive diagnostic technique has been actively pursued. Serum agglutination test remains the most popular diagnostic tool for Brucellosis (2-3). Titer above 1:160 is considered diagnostic in conjunction with a compatible clinical presentation (1-2-5) A 74 Journal of Mashhad University of Medical Sciences No. 90, Winter2006 In this patient, standard agglutination test was negative because of «prozone phenomena». But the blood and bone marrow cultures were positive for B. Melitencis. Bone marrow cultures are considered gold standard for the diagnosis of Brucellosis, since the high concentration of organism in the reticulaendothelial system (2-3-4-5) Polymerase chain reaction(PCR)- is a fast Test and can be performed on any body tissue. With positive reporting of blood and bone marrow culture of this patient Streptomycin plus Doxycyclin started. Streptomycin 10mglkg of body weight for 2 weeks and Doxycyc1in 100 mg twice daily for six weeks. No drug induced complications were seen (2). Fever disappeared rapidly and after finishing antibiotic therapy, the patient felt well, and the patient on questioning stated; before beginning of his illness he had consumed goat raw milk. Standard agglutination tube test (SAT) is a cheap simple test but sometimes blocking antibodies makes this ordinary test, negative. Class M immunoglobulin against LPS appears during the first week of infection followed by class G immunoglobulin as early as the second week. Both classes of immunoglobulin peak during the fourth week (1). Diagnosis: Brucella Melitencis.