Two thermoplastic polyolefin elastomers, Santoprene(TM) 281-82 and Sarlink(TM) 3280, were studied by small-angle neutron scattering (SANS) and swelling. Sorption was performed in 3% (volume/volume) aqueous acetic acid (HAc) solutions at 65 degrees C. Increase in mass and volume were followed separately. For SANS studies, swelling was also performed in D2O solutions of HAc. Samples were subjected to mechanical fatigue, causing mainly shear stresses. A Sarlink variety with partly deuterated mineral oil was prepared to study by SANS the influence of fatigue on distribution of the oil. Absorption of the HAc solution follows Type I Fickian diffusion. Diffusion coefficients D, calculated in three ways, revealed a discrepancy between values obtained from measurements of mass or volume increase. D values were of a 10(-13) m(2)/s order of magnitude. Influence of fatigue on D was not significant, although saturation liquid uptake differed markedly between fatigued and control samples. Also, remarkable differences between control Sarlink and Santoprene in saturation uptake were observed. From SANS experiments, no influence of fatigue on void size or distribution, or on distribution of mineral oil, could be observed. However, marked differences between control Sarlink and Santoprene was observed when data were interpreted in terms of fractal dimensions of phase boundaries.