Levels of Fyn protein are low in asymptomatic HIV infection but relative specific kinase activity is elevated. Lysate containing 5 × 10⁶ cell equivalents was immunoprecipitated with rabbit anti-Fyn and immune complexes washed and incubated with 5 μCi [γ³²P]ATP in kinase buffer containing acid-treated enolase (1.0 μg/condition). Proteins were separated by reduced SDS-PAGE and electrotransferred to Immobilon-P membranes and tyrosine-phosphorylated proteins visualized by autoradiography (Kinase Assay). Western immunoblotting was performed by probing the kinase blot with mouse anti-Fyn monoclonal antibody followed by goat-antimouse IgG conjugated to horseradish peroxidase and enhanced chemiluminescence. The relative Fyn specific kinase activity was estimated using the ratio of Fyn kinase activity (using tyrosine phosphorylation of enolase) to Fyn protein levels after densitometry analyses of the autoradiograph (Kinase Assay) and chemiluminescence blots (Western blot), respectively. The figure is representative of the results obtained with all patients and normal controls. Lanes 1 and 2 are patients with asymptomatic HIV infection, lanes 3 and 4 represent patients having AIDS, and lanes 5 and 6 are uninfected normal controls.