De novo site-specific backbone and side-chain resonance assignments are presented for U-N-15(1 -73)/U-C-13, N-15(74-108) reassembly of Escherichia coli thioredoxin by fragment complementation, determined using solid-state magic angle spinning NMR spectroscopy at 17.6 T. Backbone dihedral angles and secondary structure predicted from the statistical analysis of C-13 and N-15 chemical shifts are in general agreement with solution values for the intact full-length thioredoxin, confirming that the secondary structure is retained in the reassembled complex prepared as a poly(ethylene glycol) precipitate. The differential labeling of complementary thioredoxin fragments introduced in this work is expected to be beneficial for high-resolution structural studies of protein interfaces formed by protein assemblies by solid-state NMR spectroscopy.