Some of the most common materials normally encountered in casework were chosen: shoes, clothing, wood, and carpet materials. For comparison purposes, both indoor and outdoor experiments were conducted. Results indicate that evaporation rates, as expected, were dependent on the volatility of the fire accelerant, surrounding temperature, and absorption characteristics of the substrate. Kerosene persisted longer than gasoline on any given substrate; gasoline persisted longer on clothing outdoors at 5-15 degrees C than indoors at 22 degrees C; and gasoline and kerosene both persisted longer on canvas running shoes than on denim blue jeans. Results from the wood and carpet materials indicate that gasoline may be recovered up to 7 days after initial application; however, in this case the wood and carpet did not undergo heating due to a fire. Indigenous volatile substances from these unburned materials were also recovered using the adsorption/elution method. The results of this study may be used as a general guideline for determining the time for gasoline and kerosene to dissipate from questioned materials, but any specific case would be best served by experimentation with its given conditions. Information such as this does illustrate the importance of timeliness in sample collection by the fire investigator. 7 figures and 19 references