Urinary kallikrein excretion is known to increase in patients with nephrotic syndrome and sick cell disease, but decrease in patients with chronic kidney disease or uremia. Some of authors consider urinary kallikrein is a marker of nephropathy. To evaluate the possible role of kallikrein kinin system in chronic kidney disease, we conduct a retrospective longitudinal observation study. Patients who participating in the "Efficacy of Pentoxifylline on Chronic Kidney Disease" study are included in the study. The morning spot urinary kallikrein and cytokines are measured at the time point of 0 and 12 month in addition to clinical parameters. The correlation of urinary kallikrein and cytokine concentration will be evaluated. Using multiple regression model, the relationship of urinary kallikrein excretion with degree of proteinuria, creatinine clearance and other clinical parameter will also be evaluated.

Inclusion Criteria:

• During June 2004 and June 2005 who participate the clinical study "Efficacy of Pentoxifylline on Chronic Kidney Disease" (ClinicalTrials.gov Identifier: NCT00155246)and sign the informed consent.
• Chronic kidney disease history > 3 months, Serum creatinine: 1.1~6.0 mg/dl in female. 1.3~6.2 mg/dl in male.
• Initial Random urine protein (mg/dl) /creatinine (mg/dl) ratio > 0.5

Exclusion Criteria:

• History of allergy to pentoxifylline;
• females are nursing or pregnant;
• Obstructive uropathy;
• Unable to stop chronic immunosuppressive therapy, NSAID;
• Congestive heart failure (New York Heart Association functional class III or IV);
• Unstable angina, myocardial infarction, coronary artery bypass graft surgery, percutaneous coronary intervention, within the past 6 months prior to signing the informed consent form;
• Cerebral hemorrhage within the past 6 months prior to signing the informed consent form;
• Retinal hemorrhage within the past 6 months prior to signing the informed consent form;
• Known or suspected secondary hypertension (e.g., primary aldosteronism, renovascular hypertension, pheochromocytoma);
• Severe uncontrolled hypertension with SBP > 220 mmHg and/or DBP > 115 mmHg;
• Hepatic dysfunction as defined by the following laboratory parameters: ALT or AST > 2 times the upper limit of the normal range;
• Biliary obstructive disorders (e.g. cholestasis);
• Active malignancy