Human tissues were incubated in vitro with radiolabeled amino acids to determine whether plasma apolipoproteins are synthesized in human kidney. Subsequently, tissue extracts were screened with antisera directed against apolipoprotein E (apo E), apolipoprotein B (apo B), apolipoprotein AI (apo AI), and bulk apolipoproteins of high density lipoprotein (HDL). Newly synthesized apo E, but not apo AI or apo B, was identified in kidney and adrenal cortex. Estimates of relative rates of apo E synthesis in vitro suggest that a substantial portion of adrenal and kidney protein synthesis is committed to apo E synthesis. The relative rate of apo E synthesis was 4-6 times greater in kidney cortex than in kidney medulla. Analysis of immunoreactive apo E showed that kidney and adrenal apo E species have the same electrophoretic mobility in NaDodSO4/polyacrylamide gels as does plasma apo E. Further characterization by high resolution two-dimensional gel analysis indicated that the isoforms of newly synthesized kidney and adrenal apo E correspond to specific isoforms of plasma apo E. These findings suggest that apolipoproteins arising from peripheral tissues may play an important role in lipid transport and metabolism.