A 44-year-old woman was admitted to the hospital because of nausea, vomiting and paraplegia of both lower extremities. She was diagnosed as HIV positive in June, 2000, when she presented with retinal necrosis caused by the varicella zoster virus. Subsequently, she was started on zidovudine, lamivudine, and indinavir at a baseline CD4 positive T lymphocyte count of 16/muL, a CD8 positive T lymphocyte count of 86/muL and a HIV-RNA of 1,129,768 copies/mL. Subsequently, medication was changed to lamivudine, stavudine, lopinavir/ritonavir in April, 2002 due to leukopenia caused by the zidovudine. She remained on this medication for 8 months, prior to December 2002, when she stopped the medication 10 days before admission due to the symptoms mentioned above. In January 2000, the patient was diagnosed with chronic viral hepatitis B. She had no history of hypertension, tuberculosis or DM, and no medication other than antiretroviral drugs had been taken. On admission, the patient complained of general weakness, nausea, vomiting and paralysis of both lower extremities. However, she did not present fever, chills, abdominal pain, constipation or diarrhea. The patient's blood pressure was 110/80 mmHg, pulse rate 80/min, respiration rate 25/min, temperature 36 C. She had a chronically ill-looking appearance and an alert mental status. Conjunctivae were not pale, sclerae were not icteric and cervical lymph nodes were not palpable. On chest auscultation, breathing sounds were clear in both lungs; her heartbeat was regular without murmur. The Abdomen was soft and flat without tenderness, and bowel sounds were normoactive. The liver and spleen were not palpable and no palpable abdominal mass was found by physical examination. Muscle strength of both legs had decreased to GII, and there were no deep tendon reflexes (DTRs). Neither CVA tenderness nor pitting edema of the extremities was apparent. A laboratory examination showed a WBC of 6,920/mm2 (neutrophils 58.8%, lymphocytes 29.1%, monocytes 6.9%, eosinophils 1.3%), a Hb of 14.7 mg/dL, a hematocrit of 42.3%, and a platelet count of 159,000/mm3. Blood chemistry revealed; calcium 9.5 mg/dL, inorganic P 0.4 mg/dL, uric acid 14 mg/dL, ALP 71 IU/L, amylase 48 IU/L, lipase 111 IU/L, BUN 6.8 mg/dL, Creatinine 0.8 mg/dL, total protein 7.0 g/dL, albumin 4.7 g/dL, AST/ALT 71/60 IU/L, total bilirubin 2.7 mg/dL, direct bilirubin 1.7 mg/dL, Na/K/Cl/tCO2 135/3.1/95/8 mEq/L, total cholesterol 252 mg/dL, TG 305 mg/dL, HDL-cholesterol 16 mg/dL, LDL cholesterol 157 mg/dL, lactate 10.8 mmol/L (normal 0.5-1.6 mmol/L), and creatinine kinase 3 IU/L. Immunochemistry showed positive HBeAg, HBV DNA 1,321 pg/mL, AFP 10.61 IU/mL (normal 0-7 IU/mL), and CEA 0.566 ng/mL (normal 0-5 ng/mL). The CD4 positive T lymphocyte count was 117/muL, the CD8 positive lymphocyte count 687/muL, and a HIV-RNA level of 133,000 copies/mL. Her pregnancy test was negative, as were blood, urine and stool culture. A cerebrospinal fluid examination performed to rule out a central nervous system infection showed no significant findings, and neither did brain MRI (Figure 1). A contrast CT scan of the abdomen, performed to rule out intra-abdominal malignancy, showed only a hepatic cyst (Figure 2). Arterial blood gas analysis (ABGA) revealed a pH of 7.291, pCO2 12.6 mmHg, pO2 142.1 mmHg, SaO2 99%, and BE-ECF 20.6. Accordingly, a diagnosis of lactic acidosis was made. Intravenous sodium bicarbonate infusion and conservative treatment were immediately initiated and antiretroviral drugs were stopped. The symptoms of nausea and vomiting subsided on the third day of treatment and from the tenth day, her paraplegia of both legs also started to improve. ABGA results and lactate levels gradually normalized (Table 1) and on the 11th day, ABGA showed pH 7.474, pCO2 39.9 mmHg, pO2 79 mmHg, SaO2 96.3%, BE-ECF +5.8, and lactate 2.9 mmol/L. The patient was discharged on the 14th day without any signs of lactic acidosis. At the time of discharge, total bilirubin had decreased to 1.3 mg/dL. After discharge, antiretroviral medications were resumed in the order:- of lamivudine, efavirenz, and lopinavir/ritonavir; none of the previous symptoms recurred. Two months after discharge, her serum lactate level was 4.8 mmol/L. The patient is still on antiretroviral therapy and is being followed up on an outpatient basis.