We have investigated the possible reactions of chlorine atoms, chlorine monoxide, and hydrogen chloride with D region negative ions. The mesospheric concentrations of the neutral chlorine gases have been predicted with a diurnally varying one-dimensional model of the upper atmosphere. Despite the low abundances of chlorine compounds in air their high reactivity leads to the formation of substantial quantities of chlorine negative ions at high altitudes. The concentration of chlorine ions is limited in daylight by rapid reactions with oxygen and hydrogen atoms and at night by the competitive production of other stable ions. The presence of chlorine negative ions in the upper atomsphere is consistent with in situ mass spectrometer observations of charged species. The abundance of chlorinated ions in the D region may be correlated with mesospheric nitric oxide and water vapor concentrations.