Surfaces with p_g=q=1, K^2=8 and nonbirtional bicanonical map

We prove that if the bicanonical map of a minimal surface of general type S with p_{g}=q=1 and K^2=8 is non birational, then it is a double cover onto a rational surface. An application of this theorem is the complete classification of minimal surfaces of general type with p_{g}=q=1, K^2=8 and nonbirational bicanonical map.