The s-wave correlated pipi strength distribution in cold nuclear matte
r is investigated. The in-medium single pions are renormalized by mean
s of the usual p-wave couplings to nucleons and DELTA's. Two groups of
models for the pipi interaction are studied. The first one uses pheno
menological models which reproduce the phase shifts but do not respect
the soft-pion theorems. With increasing density a strong accumulation
of strength in the subthreshold region is observed. Slightly above sa
turation density there even occurs an instability with respect to s-wa
ve pipi pair condensation. These effects are strongly moderated or dis
appear altogether if constraints from chiral symmetry are built into t
he pipi interaction.