Pasteurization was investigated as a method of inactivating virus during the preparation of immunoglobulin for intravenous use. The effect of pH, protein concentration and the presence of protein stabilizers on the structure of immunoglobulin G (IgG) molecules during pasteurization was investigated using an immunoglobulin solution derived from a Cohn's fraction II preparation. Changes in the secondary and tertiary structure of IgG molecules as well as the degree of polymerization of protein were investigated using spectrophotometry, circular dichroism and size exclusion chromatography. Only slight changes in secondary and tertiary structure were observed after pasteurization in a 10 g L(-1) immunoglobulin solution at pH 4.5 and 5.5 in the absence of stabilizer and in a 50 g L(-1) immunoglobulin solution at pH 5.5 in the presence of glycine and sucrose or sorbitol. Concentrations of immunoglobulin solution below 20 g L(-1) were not denatured when pasteurized at pH 4.5 in the absence of stabilizers. High concentrations of immunoglobulin solution required stabilizers such as glycine and sorbitol or sucrose to prevent or reduce denaturation during pasteurization.