Infection of human peripheral blood lymphocytes by human immunodeficiency virus type 1 (HIV-1) was investigated by means of 1H nuclear magnetic resonance spectroscopy, taking advantage of the presence of signals from fluid lipid domains in the membrane of stimulated lymphocytes. A transient decrease of the lipid methylene signal intensity was observed at the time of HIV internalization, monitoring a general rearrangement of membrane structure associated with virus entry. A similar effect was also observed a few days after infection, when HIV particles are released by infected cells as demonstrated by high reverse transcriptase activity in cell supernatant. Signals arising from choline-based metabolites were also affected by HIV infection, indicating a possible slowing down of phospholipid synthesis.