Results of a two-dose (150 vs 500 mg/kg/month) crossover study with intravenous immunoglobulin (Endobulin, Immuno) (IVIG) carried out on 12 children with primary immunodeficiency syndromes over a period of 2 years are reported. Eight children had received human plasma (20 mg/kg/month) during the 2 years prior to the IVIG study. As these children had been thoroughly monitored during plasma treatment, a retrospective analysis of these data allowed for comparison with IVIG treatment. Children on low-dose IVIG therapy had significantly (P less than 0.01) fewer days with clinical illness, e.g., sinusitis, pneumonia, diarrhea, and arthritis, than did those receiving plasma treatment. High-dose IVIG therapy led to further significant clinical improvement. Lung function tests (MEF25) improved significantly as well. The difference between high- and low-dose therapy with respect to the improvement in clinical symptoms (e.g., cold, fever, otitis) was more pronounced in children with severe clinical symptoms at the initiation of the study. Children with fewer symptoms did comparably well on high- and low-dose treatment, except for those with acute febrile illness, which was less frequent in children on high-dose IVIG. Regular monitoring of liver enzymes in the group of patients on IVIG therapy gave no indication of the transmission of viral hepatitis in the course of the 2-year IVIG treatment.