Researchers estimate that over 200 accelerant-detection canines are currently assisting in fire investigations throughout the United States. On many occasions, their ability and reliability have been questioned. This study assessed 42 such teams for their ability to discriminate between common accelerants and pyrolysis products, to detect common accelerants at low concentrations, to locate accelerants precisely, and to detect various classes of accelerants. This article describes the method used to test the teams for each of these abilities. The findings show that the accuracy, dependability, and overall effectiveness of the teams varied from canine to canine and handler to handler. Effectiveness apparently depended on the canine's training, handling, and maintenance. Although most of the canine teams performed well and could be an asset to a fire investigation, some were unreliable. A universal endorsement or condemnation of all accelerant-detection canines cannot be made based on these findings; however, endorsements of specific canine teams and trainers is possible. Every working canine team should be evaluated independently. Periodic testing is necessary to establish a canine's current abilities and limitations in accelerant detection. 5 tables