In recent years, hypertonic, and hyperoncotic fluids have been examined for their potential to replace conventional isotonic fluids. This study describes the effects of commonly used intravenous fluids on immune function. The action of increased concentrations of hypertonic saline (HTS), hypertonic saline-dextran (HSD), dextran (Dx), albumin (ALB), and hydroxyethylstarch (HET) on in vitro proliferation of phytohemagglutinin-stimulated normal and prostaglandin E2-suppressed human peripheral blood mononuclear cells was tested. At clinically relevant levels, HTS, HSD (20-40 mM hypertonicity), and ALB (2.5 mg/mL) enhanced T-cell proliferation by 65, 75, and 70%, respectively. Dx and HET had little effect. HTS also reversed prostaglandin E2-suppressed (10 ng/mL) T-cell proliferation to normal levels, and HSD enhanced T-cell proliferation by 40%, in contrast to Dx, ALB, and HET which had minimal effects. The results suggest that hypertonic/hyperoncotic solutions might improve prostaglandin-mediated suppression of T-cell function in patients and may be a useful adjunct to reduce the risk of infection.