An 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. Heating, ventilating, and air conditioning (HVAC) system designers need ways to determine if a planned system will ensure the health of building occupants. Scientists will find the program useful as an experimental design aid. Building maintenance personnel will be able to use it to determine approaches that will alleviate contamination problems. Version 2 of the IAQPC extends Version 1 with more extensive input menus and output options. Improved algorithms for contaminant transport and flow have been incorporated. The program models up to six pollutants concurrently for buildings of up to 20 rooms. It allows inclusion of sources, sinks, and air cleaners and can be adapted to a wide range of structures. The algorithms used to determine the concentrations have been tested against experimental data and found to yield accurate predictions. The paper describes the model's inputs, calculations, and outputs and presents a case study performed with the model.