Degradation of 125I-labeled LDL by skin fibroblasts, EBV-lymphocytes, and monocyte-derived macrophages from individuals in family 3. Cells were preincubated for 16 hours in medium containing LPDS and then for 4 hours with 125I-labeled LDL. Saturable degradation of LDL was determined as the difference in the amount of TCA-soluble, non-iodide radioactivity in the medium of cells incubated in the presence and absence of an excess of unlabeled LDL (1 mg/ml); values are the mean of duplicate dishes. Nonsaturable degradation of LDL by normal cells was always less than 5% of the total. Data shown are representative of at least two separate experiments. (a) EBV-lymphocytes, (b) skin fibroblasts, and (c) monocyte-derived macrophages, from probands 3.1 (filled triangles) and 3.2 (open triangles) in family 3 and from unrelated normolipemic controls (filled circles).