The paper describes the initial development of sampling methods and analysis techniques for quantifying and identifying the various biological components of indoor and outdoor particulate matter (PM). Both the indoor and outdoor biological PM (BioPM) need to be measured to determine the amount originating from indoor sources and the quantity entering from the outdoors. A variety of collection substrates and filters were evaluated to assess their influence on the sampling and analysis techniques. Through these preliminary analyses, some of the difficulties presented in the methods that may be used for measuring indoor and outdoor BioPM were assessed. BioPM potentially plays two distinct and important roles in influencing the adverse health effects that have been associated with exposure to PM with aerodynamic dia less than 2.5 micrometers. Inhalation of endotoxins has been shown to increase non-specific bronchial reactivity in asthmathics. A problem in determining the importance of reducing BioPM exposure has been a lack of methods that allows the assessment of BioPM fraction of PM 2.5.