The elastic properties of rod-coil diblock copolymer poly(styrene-d(8))-b-poly(gamma-benzyl L-glutamate) (PSd-b-PBLG) rod-coil diblock copolymer solutions were investigated using small-angle neutron scattering (SANS). PBLG is known to undergo a transition from a rodlike a-helical. secondary structure to a random coil conformation under specific solvent conditions: the PBLG is (i) rodlike in dioxane and GO random coil in dioxane/trifluoroacetic acid (80/20). For the PSd-b-PBLG diblock copolymer, this conformational transition results in a topological change from a rod-coil to a coil-coil type structure. SANS results indeed show the presence of the expected scattering peaks-copolymer signature-for both conformational topologies. The position and the height of these scattering peaks are found in good agreement with a recent theoretical model that describes the conformational change in rod-coil diblock copolymer solutions. Circular dichroism experiments confirmed the change in secondary structure in the peptide block that accompanies the topological transition observed by SANS.