The viscosity of a latex sampling is determined by means of a viscometer which measures the torque produced on a specific spindle driven by an electric motor to rotate at a constant rotational frequency and at a controlled rate of shear while immersed to a specified depth in the latex. The apparent viscosity is obtained by multiplying the torque reading by a coefficient which depends on the rotational frequency and size of the spindle. Measurements may be made on the undiluted latex or on the latex after dilution to a required total-solids content.