Written by Laura Clift. (refs) point to "pycnogenol references" section.

In a study examining the anti-oxidant action of several bioflavanoids,
(-)-epicatechin 3-O-gallate and (-)-epigallocatechin 3-O-gallate were both
more potent than pycnogenol against the free radicals DPPH, superoxide anion,
OH, and OOH, although not by much (1).

The toxicity of pycnogenol is not established in published reports.
Proanthocyanidin mutagenicity is tricky, if it is completely pure it is
considered non-mutagenic. However, there is an impurity that is very similar
and hard to remove in the purification of proanthocyanidin that is mutagenic
(2).

No published work could be found on the bioavailability of pycnogenol in
particular, but oral ingestion of bioflavanoids in general results in a low
bioavailability (3).

Pycnogenol does cross the blood-brain barrier in rats when given as an
intraperitoneal injection (4). The same study seems to indicate that
pycnogenol can increase capillary resistance and decrease capillary
permeability in rats. A clinical study on 25 patients indicated an increase
in capillary resistance (5). When administered by intraperitoneal injection
to rats, chemically induced edema of the paw was decreased (6).

There are no published studies on pycnogenol's interaction with vitamin C and
most of the preventions, aids and/or cures claimed. However, procyanidol
oligomers offered no protection for venous disease from hypoxia (lack of
oxygen) (7).