Evidence of vascular leakage due to increased capillary permeability characterizes and differentiates dengue hemorrhagic fever. This article assesses the value of serum albumin for detecting vascular permeability abnormalities in dengue cases. Fourteen patients diagnosed with dengue hemorrhagic fever at two private hospitals in Recife, Brazil, between January and May 2002 were followed up with daily hematocrit and serum albumin assays. Ultrasound scans and chest X-rays were also performed. Eight (57%) of the cases presented hemoconcentration of 20% or more. Hypoalbuminemia was detected in ten patients (71%). Serum albumin assays increased the detection of permeability abnormalities in six cases (43%) in which the hemoconcentration was less than 20% and the symptoms were compatible with an exacerbated immune response. The X-rays were normal in all cases. Thus, the use serum albumin quantification increased the sensitivity of dengue hemorrhagic fever detection.