The present investigation was undertaken to apply theoretical methods to the ventilation of polluted air in a room where carbon dioxide was not homogeneously diffused. Assuming that the concentration of carbon dioxide depends on time and space, the following equation can be obtained on one and two dimensional spaces in a room (Subscripts denote spaces in a room). a-exp[log{C (t)/C (0)}/t] where a is a ventilation constant (a〓0), and C (t) and C (0) are the concentration of carbon dioxide at t and t=0, respectively. When ventilation was carried out with evolution of carbon dioxide, the following equation is obtained : log α=log[{C (t+10)-C (t)}/{C (t)-C (t-10)}]/10 where α is also a ventilation constant and C (t+10) and C (t-10) are concentrations of carbon dioxide at time t+10 min and t-10 min, respectively. According to a difference method, the following equation is obtained : U (t)={(A-B)+(A+B) (1-2a)t}/2 where U (t) is the concentration of carbon dioxide in the room at time t, and A and B are concentrations of carbon dioxide in the room and outdoor at t=0, respectively. It was found that above equation was available for the theoretical study of ventilation of polluted air diffused heterogeneously in room.