  The PICASSO experiment reports an improved limit for the existence of cold
dark matter WIMPs interacting via spin-dependent interactions with nuclei. The
experiment is installed in the Sudbury Neutrino Observatory at a depth of 2070
m. With superheated C4F10 droplets as the active material, and an exposure of
1.98+-0.19 kgd, no evidence for a WIMP signal was found. For a WIMP mass of 29
GeV/c2, limits on the spin-dependent cross section on protons of sigma_p = 1.31
pb and on neutrons of sigma_n = 21.5 pb have been obtained at 90% C.L. In both
cases, some new parameter space in the region of WIMP masses below 20 GeV/c2
has now been ruled out. The results of these measurements are also presented in
terms of limits on the effective WIMP-proton and neutron coupling strengths a_p
and a_n.
