Small specimens of nylon 6/PDMS compositions were screened for relative levels of toughness using a micromechanical testing device. Measurements were made of the total crack length emanating from pre-cut notches in a specially designed specimen. At room temperature, cracks propagated readily in nylon 6 homopolymer and somewhat more slowly in a composition containing 4 wt% PDMS; at 10 and 28 wt% PDMS the cracks were blunted in a diffuse whitened zone and did not propagate through the specimens. At -40 degrees C, the 10 wt% blend appeared to be as tough as the 4 wt% blend at room temperature.