By using abdominal ultrasonography (UlS), deep nodes were detected in 41 of 85 (48%) HIV-1 positive subjects, most of them heroin addicts, but in none of 85 healthy HIV-negative controls. Computerized tomography, performed in 10 cases of lymphadenopathy, invariably confirmed the UlS findings. Prevalence [asymptomatic carriers: 8/15 (53%); PGL patients: 8/18 (44%); ARC: 13/27 (48%); AIDS: 12/25 (48%)], number, size, and site of deep nodes were comparable among the different CDC groups. No correlation was found between abdominal and superficial lymphadenopathy. Median serum concentrations of gammaglobulins (g/dl) and IgG (mg/dl) were higher in patients with than without deep nodes (2.25 vs 1.87 and 2540 vs 1900, respectively) (p < 0.01) as well as in cases with than without superficial nodes (2.15 vs 1.80 and 2340 vs 1941, respectively) (p < 0.05). Abdominal lymphadenopathy occurred during all stages of HIV infection even in asymptomatic carriers: this should be considered in the differential diagnosis of UlS-detected deep nodes. Enlargement of either deep or superficial nodes seems to reflect a state of polyclonal B cell activation.