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Abstract: We discuss a simple approach to enhance sensitivity for 13C high-resolution solid-state NMR for proteins in microcrystals by reducing 1H T 1 relaxation times with paramagnetic relaxation reagents. It was shown that 1H T 1 values can be reduced from 0.4–0.8s to 60–70ms for ubiquitin and lysozyme in D2O in the presence of 10mM Cu(II)Na2EDTA without substantial degradation of the resolution in 13C CPMAS spectra. Faster signal accumulation using the shorter 1H T 1 attained by paramagnetic doping provided sensitivity enhancements of 1.4–2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0–8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13C high-resolution solid-state NMR spectroscopy. [Copyright &y& Elsevier]