The Indoor Air Quality Simulator for personal computers (IAQPC) has been developed in response to the growing need for quick, accurate predictions of indoor air contamination levels. Many building energy use programs are currently in use, but heating, ventilating, and air conditioning (HVAC) system designers need a way to determine if a planned system will ensure the health of building occupants. Scientists will find this program useful as an experimental design aid, and building personnel will be able to use it to determine approaches that will alleviate contamination problems. This program models up to six pollutants concurrently for buildings of up to 20 rooms. Most single-story buildings can be adapted to one of the six available floor plans. Buildings with more than one story may be modeled if the stack effects can be ignored. IAQPC allows inclusion of sources, sinks, and air cleaners in the rooms and in the HVAC system. Up to eight sources, four sinks, and two air cleaners can be described, then selected for the individual rooms. In addition to the room air cleaners, up to two types may be selected for the HVAC system. Outdoor air concentrations are specified and the method for determining initial indoor concentrations is chosen. Air flows are calculated by the program based on the cross-sectional interconnections between the rooms, the HVAC system, and the outdoor air. The total flow through the system is specified, then an iterative approach determines the flows. The improved algorithms used to determine the concentrations have been tested against experimental data and found to yield accurate predictions in a fraction of the time necessary for other current models. This paper will describe the model's inputs, calculations, and outputs.