An experiment designed to quantify probe-induced aerodynamic perturbations to in-cylinder sampling measurements in a motored engine is discussed. Good agreement was observed between concentration measurements obtained with a sampling probe utilizing a flame ionization detector and those obtained by laser Raman scattering at the probe tip. However, large differences were found between the Raman-measured concentration profiles obtained with and without the probe installed in the engine. These differences occurred because of probe-induced perturbations to the in-cylinder air motion which decreased the mean velocity and increased local mixing rates. Effects due to probe orientation in the flow, probe insertion depth, probe inflow, and far-field flow perturbations are reported.