  The near threshold production of K+K- pairs in proton-proton collisions has
been investigated at the cooler synchrotron COSY below and above the threshold
for the $\phi$ meson using the COSY-11 and ANKE facilities, respectively. The
excitation function determined for the pp-->ppK+K- reaction revealed a
statistically significant enhancement close to the threshold which may
plausibly be assigned to the influence of the K-p interaction. In addition,
observed consistently by both groups, a strong enhancement at low values of the
ratio of the K-p to K+p invariant mass distributions shows that the proton
interacts much stronger with K- than with K+. In this report we focus on the
measurements performed by the COSY-11 collaboration. We explain the
experimental method used and present main results of completed analyses as well
as a new qualitative elaboration of the ppK+K- events population on the
Goldhaber plot. We conclude with the observation that event densities increase
at the region where the influence from the K+K- interaction is expected.
