The pattern of serum lipids and lipoproteins was investigated before and after surgery in 77 patients with respect to the "acute-phase reaction". Special attention was paid to the severity of the surgical trauma and the time course of postoperative alterations. Therefore, 12 different serum parameters were measured in 18 patients just before surgery and on days 1, 3, 5 and 10. From the results of this sample, patients in the main trial were divided into three groups with different degrees of trauma: group 1 (n = 22) with low surgical trauma; group 2 (n = 20) with extensive abdominal operations; group 3 (n = 17) with total endoprosthesis of the hip. A 25-40% perioperative decrease in cholesterol, triglycerides, lipoprotein classes (alpha-, beta- and pre-beta-lipoproteins) and apolipoprotein A1 and B was found during the first 24 h after surgical trauma. Thereafter, the above parameters showed a tendency toward more or less complete normalization by day 10. In contrast, C-reactive protein (CRP), initially increased by a factor of 8-10, returned to the normal concentration range by postoperative day 10. The amount of cholesterol loss was low in group 1 (-16%), but considerable in group 2 (-38%) and group 3 (-35%) when compared with preoperative levels. This cholesterol loss was mainly due to a decrease in beta-lipoproteins (LDL), but also in alpha-lipoproteins (HDL). It can be concluded from these results that a sudden decrease in cholesterol containing serum lipoproteins occurs in relation to the size of a surgical trauma.(ABSTRACT TRUNCATED AT 250 WORDS)