The computer programs published so far enabled the computation of airflows assuming constant temperatures or the calculation of air temperatures assuming constant airflows. Recently, a new microcomputer program was developed in which thermal conditions were considered when predicting the spread of contaminants in buildings. The program enabled simultaneous dynamic simulations of contaminant distribution, airflows, and temperatures in a multizone building. Using the new program, the dynamic distributions of contaminant concentration and air quality in an example building were determined with and without the recirculation of ventilation air, with different thermal loads and with several door positions. For comparison, some simulations were repeated in isothermal conditions. The results showed that a high thermal load increased the spread of contaminant. Recirculation of the ventilation air had a deteriorative impact on the air quality in the simulated building. There was a clear difference in the air qualities predicted by the respective simulations carried out with and without thermal analysis. It is believed that the inclusion of thermal analysis considerably improved the calculation method for the evalution of contaminant distribution in a building.