The potentiostatic electrochemical template synthesis of nanowires (Ni, Co, Cu, Au, and polyporrole) in polycarbonate track-etched membranes with nominal pore diameters d(N) between 10 and 200 nm is studied. Along the wire the cross section is found to vary : the wire diameter, which is argued to directly reflect the pore diameter, is observed (for all deposits) to be substantially larger in the middle than at both ends. Therefore, the pores are not cylindrical with constant cross-section, in general, but appear to be "cigarlike". Inside the membrane, the pores are wider by up to a factor 3. Comparing the potentiostatically measured current-time characteristics obtained during wire growth for different pore dimensions, a pore-size-dependence of the diffusion coefficient D for the metal ions is found:; D = 2.5, 1.5, and 0.7 x 10(-6) cm(2)/s for d(N) = 80; 30, End 10 nm, respectively.