We report the use of targeted p- and n-type chemical perturbations to manipulate high-TC ferromagnetism in Mn2+∶ZnO and Co2+∶ZnO in predictable and reproducible ways. We demonstrate a clear correlation between nitrogen and high-TC ferromagnetism for Mn2+∶ZnO and an inverse correlation for Co2+∶ZnO, both as predicted by recent theoretical models. These chemical perturbations reveal rich possibilities for exerting external control over high-TC spin ordering in diluted magnetic semiconductors.