Twenty seven children with hematological malignancies were treated with Sandoglobulin for life threatening infections due to severe granulocytopenia. We have studied the opsonic activity of sera in patients before and 7,14 and 21 days after the infusion of Sandoglobulin. Before the therapy a decrease of serum opsonic activity at the stage of ingestion and intracellular killing of bacteria has been shown. It was due to a deficiency of opsonizing factors. After treatment with Sandoglobulin the significant improvement of the opsonic activity of tested sera was found, but only at the stage of the ingestion of bacteria. The optimal interrelationship between opsonizing capacity of sera at the ingestion and intracellular killing phase was observed in the group of children treated with the relatively low Sandoglobulin dose (0.3-0.6 g/kg). In patients with the longest infection duration, who received the high Sandoglobulin doses (> 0.6 g/kg), the largest percentage of sera containing immune complexes was detected. These data demonstrate that high doses of globulins should be administered with certain care.