• Circulating immune complexes (CIC) were analyzed in a cohort of 30 children infected with the human immunodeficiency virus. Elevated CIC were detected by the C1 q assay in 70% (21/30) of all patients and by the Raji cell assay in 93% (28/30) of all patients. While only less than one third of patients with elevated CIC had free serum antibodies to Epstein-Barr virus, 80% (16/20) of them had detectable antibodies to Epstein-Barr virus associated with CIC. Enriched CIC in human immunodeficiency virus–infected children contained low levels of complement. These findings document that, as an expression of the humoral immunodeficiency, CIC in human immunodeficiency virus–infected children are deficient in complement and can thus be underestimated if complement-precipitating methods are used for their detection.