We evaluated the opsonic activities of human intravenous immunoglobulin (IVIG) preparations against pathogenic organisms by measuring the luminol-enhanced chemiluminescence (CL) from human polymorphonuclear leukocytes (PMN) during the phagocytosis of these organisms. Polyethylenglycol-treated IVIG significantly increased the CL of PMN by opsonization against various bacteria and Candida albicans (p less than 0.01). The high CL induced by IVIG with intact Fc-fragment showed no significant differences among lots or preparations made by different treatments. In both PMN-CL in the absence of human serum and whole blood CL at low concentration of serum complement, the CL response was not affected by pepsin-treated IVIG. In the severely burned patients' blood with a very low concentration of serum immunoglobulin, IVIG with intact Fc-fragment significantly increased CL (p less than 0.01). It is suggested that administration of IVIG is useful against infections in these patients. The measurement of whole blood CL in vitro may be useful for evaluating the opsonic activity of IVIG against target pathogens in vivo.