OBJECTIVE To determine in vitro the compatibility of reconstituted intravenous immunoglobulin (IVIG) (Gammagard, Baxter-Hyland) with five different neonatal and pediatric intravenous solutions in Viaflex polyvinyl chloride bags. METHODS In vitro compatibility study. METHODS Samples were taken at time = 0, 10, 30, 60, 90, and 120 minutes and at 4, 8, 12, and 24 hours and assayed for total immunoglobulin G content and antibodies to hepatitis B surface antigen. Type III group B Streptococcus (GBS) and opsonic activity for type III GBS were analyzed at time = 0, 60, and 120 minutes and 12 and 24 hours. All results were compared with those from pure IVIG. RESULTS Our results demonstrate that mixing IVIG with intravenous solutions commonly used in the care of premature infants (dextrose 5% in water [D5W], D15W, D5W/NaCl 0.225%, and total parenteral nutrition [TPN]) does not significantly alter total immunoglobulin G concentrations or concentration of antibodies to hepatitis B surface antigen or type III GBS. As well, the in vitro functional activity for type III GBS of the IVIG, when mixed with these solutions for up to 24 hours, remained intact. An apparent decrease in bactericidal killing was seen with the IVIG/central TPN mixture. This apparent decrease was found to be an artifact of the high concentration of glucose (20 percent) in the solution. CONCLUSIONS We propose that Gammagard may be mixed with these solutions through Y-site connections without loss of antibody content or functional activity of the IVIG.