CuZSM5 catalysts, prepared by ion exchange of HZSM5 (Si/Al=80), enable selective lean NOx reduction at the spark ignition engine exhaust. All catalysts, even if exchanged to very high copper loading (556% apparent exchange level) give no evidence for segregated copper oxide phases. In the presence of water they are easily reduced in vacuum at 550 degrees C and are stable to redox cycles (O-2, vacuum) treatments. Increasing Cu content to about 200% apparent exchange level results in increasing NOx, CO and HC conversions. From 200 to 550% exchange CuZSM5 catalysts give similar performances. Preliminary investigation shows that after catalytic tests there is evidence for CuO formation only in the copper-richest catalysts.