Maritime pine bark extract is monographed in the United States Pharmacopeia (USP) as a dietary supplement. As knowledge about active principles - protein interactions contribute to insights into pharmacokinetic and pharmacodynamic properties we elucidated the plasma protein binding of various constituents and metabolites of this extract. We chose high performance affinity chromatography for fast characterization of the analytes' binding extent to human serum albumin. For selected maritime pine bark compounds that were previously detected in human plasma samples we additionally employed ultrafiltration. The flavonoids catechin and taxifolin revealed highest plasma protein binding of close to 100%, followed by procyanidin B1 and the cinnamic acid derivates ferulic acid (73.5 ± 0.12%), caffeic acid (66.0 ± 0.23%) and p-cumaric acid (65.4 ± 4.84%). Lower protein binding was observed for the benzoic acid derivates vanillic acid (56.3 ± 1.16%), p-hydroxy benzoic acid (35.3 ± 10.9%), gallic acid (31.6 ± 0.56%) and protocatechuic acid (20.7 ± 0.09%). Lowest protein binding was measured for the maritime pine bark metabolites δ-(3,4-dihydroxy-phenyl)-γ-valerolactone (34.9 ± 1.28%) and δ-(3-methoxy-4-hydroxy-phenyl)-γ-valerolactone (26.4 ± 0.03%). For all but one compound the results of both methods revealed excellent correlation. Thus, we provide new data as a basis for a more comprehensive understanding of the bioactivity of a complex plant extract.