Abstract: A method for the detection of chemical agent present in a material comprising exposing a calixarene, having redox active substituents on its para rim, to a solution or suspension derived by admixture of all or some of the material with a liquid measuring any change in electrical behavior of the calixarene during or after exposure to the solution or suspension as compared to a reference condition, and relating such change in electrical behavior to the presence of chemical agent. Preferably, the calixarene exposed to the solution or suspension is a calix?4!arene or general formula (J), wherein Y.sup.1 to Y.sup.4 are independently selected from hydrogen, alkyl, alkenyl, aryl, aralkyl or a redox active substituent and R.sup.1 to R.sup.4 are independently selected from hydrogen, alkyl, alkenyl, aryl, aralkyl, or a polymerisable moiety, wherein at least one of Y.sup.1 to Y.sup.4 is a redox active substituent.