The aim of this study was to evaluate the nutritional status of adults with HIV infection or with AIDS through the use of biochemical parameters. The study was performed on 43 patients (19 HIV+ and 24 AIDS patients), between 26 and 44 years of age, from low and medium socioeconomic status, with access to health care services; 35 patients were under highly active antiretroviral therapy (HAART) treatment. Body weight and height were determined, and the Body Mass Index calculated (kg/m2). Blood samples were collected from fasting patients. Plasma cholesterol (total, HDL and LDL), triacylglycerol, total protein, apolipoproteins A-I and B, albumin, transthyretin, retinol binding protein, and ceruloplasmin concentrations were determined. Plasma levels of zinc, copper, and selenium were determined in a haemolysis-free sample by flame atomic absorption spectrometry. Statistical analyses were performed with the Student's t-test. AIDS patients showed changes in biochemical parameters, particularly an increase in fibrinogen and a trend to decreased transthyretin levels. These findings stress the importance of the inclusion of functional biochemical parameters in the periodic evaluation of these patients. This would allow an early assessment of the need for appropriate nutritional support, implemented along with the specific retroviral treatment. This would aim at delaying the progression of the disease, and might improve the prospects of survival and quality of life.