Hepatocellular heterogeneity of biochemical function is well established for many aspects of liver metabolism. This study addresses the question of cellular heterogeneity in the catabolism of low-density lipoprotein by rat hepatocytes. Low-density lipoprotein binding (4" C) and uptake (37" C) by rat hepatocytes were studied by use of human low-density lipoprotein labeled with a highly fluorescent lipophilic probe, N,N-dipentadecylaminostyrylpyridinium iodide, recently developed by us. Single-cell suspensions derived from rat hepatocytes in primary culture and from liver perfusion were studied with flow cytometry with and an approximation algorithm for data analysis. These studies show subpopulations of cells negative and positive for the specific binding and uptake of low-density lipoprotein. Dissociation constants for low-density lipoprotein binding and uptake were determined for the total population (18 pglml, binding; 12 pglml, uptake) and found to be in good agreement with previously reported values. Additionally, the dissociation constant for binding for the positive subpopulation was determined and found to be 3 pg/ml. This lower value is more typical of the values seen in other cell types. These findings are strongly suggestive of functional heterogeneity in the hepatic catabolism of low-density lipoprotein.