The reactions of the cyanomethylene (HCCN) radical with nitric oxide (NO) and with molecular oxygen (O-2) have been investigated using infrared kinetic spectroscopy. The overall second-order rare constant for each reaction has been determined using pseudo-first-order methods yielding (3.5 +/- 0.6) x 10(-11) cm(3) molecule(-1) s(-1) for the reaction with NO and (1.8 +/- 0.4) x 10(-12) cm(3) molecule(-1) s(-1) for the reaction with O-2. For each reaction, several products were observed, but none were quantified. Hydrogen cyanide (HCN) and fulminic acid (HCNO) were observed as products of the reaction with NO. For the reaction with O-2, HCN, hydrogen isocyanide (HNC), and carbon dioxide (CO2) were observed. Species searched for but not detected from either reaction include isocyanic acid (HNCO), cyanic acid (HOCN), formyl (HCO) radical, isofulminic acid (HONC), hydroxyl radical (OH), and ethynyl radical (C2H). In addition, NO was searched for, but not observed, as a product of the O-2 reaction. On the time scale of our experiments, no reaction between HCCN and any of the following species was observed (k < 10(-13)) cm(3) molecule(-1) s(-1)) : methane (CH4), CO2, acetylene (C2H2), ethylene (C2H4), carbon monoxide (CO), and hydrogen (H-2).