A vibrating-wire technique has been used to directly measure the viscosity increase in a dilute 3-4He solution caused by brute-force spin polarization up to 40%. The viscosity of a solution with degeneracy temperature TF=19.5 mK was measured over the temperature range 6.1–100 mK in magnetic fields of 1.00 and 7.96 T. Spin polarization caused a marked decrease in the mechanical Q of the viscometer at low temperatures. The observed viscosity is compared with calculations of the transport coefficients of dilute quantum gases for all temperatures and spin polarizations.