The present invention provides a system for the improved detection of ecstasy-class compounds in biological samples. New ecstasy-class analogs are provided for detection of such ecstasy-class drugs. These analogs are compounds, or salts thereof, of a 2-amino-methylenedioxyphenyl (MDP) derivative attached to Z, where Z is a moiety capable of bonding, either directly or indirectly, with an immunogenic carrier, a detectable label, or a solid capture vehicle. Such analogs may be used to construct immunogens, enzyme or enzyme-donor conjugates, and other conjugates. The immunogens reproducibly generate antibodies with an exquisite ability to distinguish various ecstasy-class drugs in biological samples from potentially interfering substances. The specific antibodies and the conjugates may be used to distinguish and measure various ecstasy-class compounds in biological samples, such as those obtained from an individual suspected of substance abuse. In another aspect, the invention includes certain reagents, reagent combinations, and kits for performing assay methods for ecstasy-class compounds in a biological sample.