Antigenemia is commonly detected in children with acute rotavirus diarrhea, but the prevalence of viremia has not been clearly defined. We examined antigenemia in plasma and RNAemia in peripheral blood mononuclear cells (PBMC) of children with acute diarrhea by EIA, RT-PCR, and Southern hybridization, using primers and a probe specific to rotavirus NSP4 gene. We detected the presence of rotavirus antigen in 33.3% and almost full-length NSP4 gene in 70.8% of the acute-phase plasma and PBMC, respectively. In contrast, antigenemia and RNAemia were detected in 0% and 4.2% of the convalescent-phase plasma and PBMC, respectively, which were similar to antigenemia (0%) and RNAemia (7.7%) in healthy controls. We demonstrated an increase in the proportions of activated myeloid dendritic cells (mDC) and activated plasmacytoid DC (pDC) in acute-phase PBMC of patients when compared to those in convalescent phase of patients and in PBMC of healthy controls. The activation of mDC peaked on days 2–4 after illness onset, and the activation of acute-phase pDC appeared to correlate with levels of antigenemia. High prevalence of NSP4 gene in acute-phase PBMC indicates possible rotavirus replication in white blood cells, and extraintestinal spread and the activation of DC may have implications for the prevention of rotavirus disease in children.