A method for reducing RNA and DNA in the bacterium Methylococcus capsulatus (Bath) has been developed. Endogenous RNase and DNase were activated by a 10 s heat shock at 90 degrees C. Cells were then incubated at 60 degrees C for 20 min to allow degradation of the nucleic acids. The optimum pH for the process was 7.0. The protein loss was less than 10% and occurred during the initial heat shock. No protein loss was found during incubation. The total dry-weight loss in connection with an 80% reduction of the nucleic acid content was 20%-25%, giving a final product with a raw protein content of approximately 75%. Reduction of both RNA and DNA was inhibited by CuSO4 and ZnSO4. DNA reduction was stimulated by minerals. Optimal stimulation was found at FeSO4. Reduction of RNA was not increased by any of the minerals tested.