In plasma, the bulk of apoSAA, a positive acute phase reactant protein, is transported in high density lipoproteins (HDL), especially HDLH (apoA1-rich HDL). In this study we tested whether apoA1 deficiency would adversely affect apoSAA concentration and lipid distribution in mouse plasma lipoproteins. Acute phase response (APR) was induced in C57BL/6J (apoA1+/+) and apoA1-knockout mice (apoA1-/-) by a subcutaneous injection of silver nitrate. The APR increased cholesterol concentrations in LDL of apoA1-/- mice and apoA1+/+ mice in a like manner. In contrast to apoA1+/+ mice, concentrations of cholesterol, phospholipids and proteins in both HDLL (1.063<d<1.103 g/ml) and HDLH (1.103<d<1.21 g/ml) were significantly increased by the APR in apoA1-/- mice. Total concentration of plasma apoSAA and its distribution in lipoprotein fractions was similar in both APR groups. The bulk of plasma apoSAA was contained in HDL and not in VLDL or LDL even when the HDL concentration was low. In apoA1-/- mice, HDLL and HDLH contained more apoSAA than in apoA1+/+ mice. These results indicate that apoA1-/- mice are not deterred from mounting an apoSAA response similar to apoA1+/+ mice and that apoA1-rich HDL particles are not necessary for apoSAA transport in the plasma.