Cross sections for 1ƒ7/2 neutron- and proton-transfer reactions on 48Ca have been measured. A distorted-wave Born approximation analysis of these and other similar results for a 40Ca target reveals isotope shifts of the 1ƒ7/2 rms radii which are about 0.2 fm in magnitude and have opposite signs for neutrons and protons. These shifts are in a reasonably good agreement with calculations based on average isospin dependent single-particle potentials. NUCLEAR REACTIONS 48Ca(3He,d0), E3He=8-10 MeV, 48Ca(d, t0), Ed=8.5 MeV. Measured σ(E, θ). DWBA analysis, comparisons with 40Ca(t, d0) and 40Ca(3He, d0). Deduced isotope shifts of rms radii of 1fƒ7/2 neutrons and protons.