The concentration of LDL free in the IF from normal intima is twice the concentration in the patients plasma. LDL is virtually excluded from media, thus it seems to be trapped between endothelium and the internal elastic lamina. Expressed as percent of plasma concentration, concentration of macromolecules in IF is directly related to molecular mass suggesting molecular sieving. There appears to be specific reversible association of fibronectin with tissue components, but not of LDL. In IF from early proliferative (gelatinous) lesions LDL concentration increased by an average of only 30%, and in some samples it was decreased, suggesting that it was not the stimulating factor. There was a slight decrease in its net negative charge. Numerous fat-filled cells totally depleted IF of LDL. The net negative charge of LDL from samples containing fat-filled cells was the same as adjacent normal intima.