The carbonate radical (CO3 center dot-) is of importance in biology and chemistry. We used pulse radiolysis to generate the CO3 center dot-radical and show there is no reaction with oxygen. However, in the presence of ammonia the CO3 center dot- radical is removed by NO center dot, which itself arises from the scavenging of NH2 center dot by oxygen, and the mechanism of this process is reported. The CO3 center dot- radical shows complex decay patterns in the presence of ammonia, which can be understood as a balance between the radical-radical reaction CO3 center dot- + CO3 center dot- and CO3 center dot- + NH2 center dot (the amino radical). Also, we report reactivity with glycine and alanine and with melanin models. The CO3 center dot- reacts with both dopa-melanin (DM, a model of black eumelanin) and with cysteinyldopa-melanin (CDM, a model of red/blond phaeomelanin). However, the reaction rate constant is much higher with CDM than with DM.