NARK II Duquenois-Levine Reagent (Marijuana/Hashish Hash-Oil/THC) This presumptive test is designed to identify THC in Marijuana. Court acceptance of the Duquenois-Levine Reagent has been established through Frye Hearings and is the singularly most reliable field test manufactured. To eliminate potential false positives, always agitate the 1st ampoule sixty (60) seconds before continuing with the 2nd and 3rd ampoules. Like all our NARK II narcotic field tests, the Duquenois-Levine Reagent is meant for presumptive field drug testing. 10 tests/box.