To study the interrelations between the changes of acute phase proteins and those of serum lipoproteins in acute infections we measured the concentrations of different lipoproteins, serum amyloid-A protein and C-reactive protein and activities of lipoprotein lipase and hepatic lipase during acute and convalescence phase and after complete recovery in 64 patients with infectious diseases (30 with viral infection and 34 with bacterial infection). The maximal decrements of both low density lipoprotein and high density lipoprotein cholesterol correlated significantly with the acute phase levels of C-reactive protein and serum amyloid-A protein. The acute phase concentration of very low density lipoprotein triglyceride correlated inversely to C-reactive protein level (r = -0.31, P less than 0.05) but not to serum amyloid-A protein level. Regression analysis showed that the concentration of C-reactive protein was a significant predictor of very low density lipoprotein triglyceride level in the acute phase of infection but not during convalescence. These results and the previous findings that C-reactive protein binds to low and very low density lipoproteins and that serum amyloid-A protein is associated with high density lipoprotein give credence to the view that C-reactive protein and serum amyloid-A protein interfere with the metabolism of serum lipoproteins during acute phase of infection.