n-Hexane zero-concentration diffusivity in high density polyethylene obtained 'indirectly' from integral desorption measurements using the free volume concept was compared with the zero-concentration diffusivity obtained directly at low-n-hexane activities using a quartz-ring system. The difference between the results obtained by the indirect and direct methods was within the experimental error. The concentration dependence of the diffusivity predicted by the Cohen-Turnll-Fujita free volume theory was in accordance with experimental data.