SummaryThe effect of various lipids, proteins, and other substances on the adsorption rate of dipalmitoyl phosphatidylcholine (DPC) was investigated. Each substance was added to a sonicated suspension of DPC in saline, and the surface pressure of the adsorbed surface film was measured using a platinum plate suspended from an electrobalance. Pure DPC adsorbed very slowly, being complete only after 8 hr; its half-adsorption time was 91.8 ± 8.3 min. Four additives markedly reduced the half-adsorption time of DPC: dipalmitoyl phosphatidylglycerol (1.1 ± 0.2 min), phosphatidylinositol (2.8 ± 0.4 min), serum high-density lipoprotein (1.0 ± 0.2 min), and surfactant apoprotein (0.9 ± 0.1 min). The half-adsorption times of mixtures of DPC and the other additives ranged from 15.3 ± 1.9 to 107.8 ± 12.1 min.