The invention provides a hapten derivatized with a crosslinker at the nitrogen of the 8.beta.-carboxamide of 2-oxo-3-hydroxy LSD. The invention also provides an immunogen comprising the aforementioned hapten coupled to an antigenicity-conferring carrier material; a conjugate comprising the aforementioned hapten coupled to a labelling agent, as well as, antibodies raised against the aforementioned immunogen and capable of binding with at least the 3-hydroxy-2-pyrrolidone structural epitope of 2-oxo-3-hydroxy LSD.