The spin-transfer effect has been studied in magnetic tunnel junctions (PtMn/CoFe/Ru/CoFe/Al2O3/CoFe/NiFe) with dimensions down to 0.1×0.2 μm2 and resistance–area product RA in the range of 0.5–10 Ω μm2 (ΔR/R=1%–20%). Current-induced magnetization switching is observed with a critical current density of about 8×106 A/cm2. The attribution of the switching to the spin-transfer effect is supported by a current-induced ΔR/R value identical to the one obtained from the R versus H measurements. Furthermore, the critical switching current density has clear dependence on the applied magnetic field, consistent with what has been observed previously in the case of spin-transfer-induced switching in metallic multilayer systems. © 2004 American Institute of Physics.