The effect of hydrogen addition on HCN production by the ammoxidation of methane over Pt-Rh gauze catalyst has been examined. Upon adding small amounts of H-2, the HCN selectivity increased from similar to 74 to 82% on NH3 basis at 35% N-2 dilution and (CH4+NH3)/O-2=2, while selectivities on CH4 basis were nearly unchanged. Using air instead of oxygen, the HCN selectivity increased from 76 to 86%. However, the increase in HCN selectivity with H-2 addition was accompanied by a decrease in the NH3 conversion. H-2 addition with different (CH4+NH3)/O-2 and CH4/NH3 ratios and with preheating of feed gases has also been investigated. The H-2 produced was observed to be greater than that fed for all conditions, so that with recycle the process would require no additional source of H-2. Experimental results obtained here can be qualitatively explained on the basis of a surface reaction model for Andrussow reactor described previously.