Delipidated high density lipoprotein (apo-HDL), isolated apolipoproteins apoA-I and apoA-II, Scarboxymethylated apoA-II, apoC-I1, the NH2-and CO-OH-terminal CNBr peptides of apoA-II, and the COOH_ terminal CNBr peptide of apoA-I were recombined in vitro with [N-C3H3-cholinelphosphatidylcholine (PC) and (SPM). The It has been shown (1-4) that the protein moiety of human serum high density lipoprotein (HDL), prepared in its lipidfree form (apoHDL) by treatment with organic solvents (5, 6) retains its capacity to bind lipids, both in vivo (7) and in vitro (3,8). About 90% of the protein moiety of apoHDL is composed of two major apoproteins, designated as apoA-I and apoA-II, or, by their COOH-terminal amino acids, as apoGln-I and apoGln-JI (9-16); the remaining 10% is mainly composed of three minor apoproteins (apoC-I, apoC-II, and apoC-III), also associated with the very low density lipolprotein family (9). The complete amino-acid sequences of apoA-II, apoC-I, and apoC-III have been reported (17)(18)(19) 1.063 and 1.210 g/ml, and delipidated with chloroformmethanol, 2:1 (6). The procedures used in the isolation and characterization of the individual proteins of apoHDL are described elsewhere (6). ApoA-I was isolated by chromatography of apoHDL in 6 M urea on Sephadex G-200 (Pharmacia, superfine) (13). ApoA-II was isolated by chromatography of apoHDL in 6 M'\ urea on DEAE-cellulose (Whatman, DE-52) (6, 12). ApoC-III was isolated as described (27,28). Cleavage with CNBr (Eastman, ratio of reagent to peptide, 500: 1) was performed in 70% formic acid at 250 for 48 hr (29). The resulting peptide fragments of apoA-II were purified to homogeneity by chromatography on Sephadex G-75 (0.2 M Tris*HCI, pH 8.6, 6 M urea); peptides of apoA-I, by chromatography on Biogel P-10 (25% acetic acid). ApoA-I, apoA-IJ, COOH-and