The use of copolymers obtained by free-radical polymerization of a mixture
of
i) 0.1 to 40% by weight of an olefine, and
ii) 60 to 99.9% by weight of N-vinyl lactam,
with the proviso that the total of components i), ii) and iii) equals 100%
by weight, as solubilizers for slightly water-soluble bioactive
substances.