In this paper, we report on a considerable (up to about 18%) magnetoresistance (MR) effect in glass-coated Co-Cu microwires prepared from immiscible elements. Samples of Co/sub 10/Cu/sub 90/ microwires with a metallic nucleus diameter of 3-17 /spl mu/m and total diameter up to 25 /spl mu/m were prepared by the Taylor-Ulitovsky technique. The Co/sub 10/Cu/sub 90/ microwires generally consist of nanocrystals of Co and Cu with average grain size of about 40 nm, although the Co-phase content depends on the microwire geometry (metallic nucleus radius and glass-coating thickness). The magnetic field dependence of MR is completely anhysteretic, showing monotonous decay with the magnetic field.