impact the predictions for the level of astrometric and flux perturbations produced by dark matter substructures in gravitational lenses [@rozoetal06; @chenetal07]. Here, we wish to estimate the level at which the projected substructure mass fraction of lensing halos could be affected due to lensing biasing.

The paper is organized as follows: in section \[sec:biases\] we derive the basic equations needed to compute how observable quantities will be biased in lensing galaxy samples due to halo triaxiality. Section \[sec:model\] presents the model used in this work to quantitatively estimate the level of these biases, and discusses how lensing halos are oriented relative to the line of sight as a function of the halos’ axes ratios. Section \[sec:axis\] investigates the projected axis ratio distributions of lensing versus non-lensing galaxies, and demonstrates that present day lensing samples are too small to detect the triaxiality induced biases we have predicted. Section \[sec:ratio\] discusses the problem of the quad to double ratio, and section \[sec:subs\] demonstrates that halo triaxiality biases the projected substructure mass fraction in lensing halos by a negligible amount. Section \[sec:caveats\] discusses a few of the effects we have ignored in our work and how these may alter our results, and finally 