Simple solid-state colorimetric sensors for precursors used in and toxic by-products of metal organic vapour-phase epitaxy (MOVPE) of mercury cadmium telluride (MCT) are described. 2,2'-Bipyridine and its commercially available 4,4'-dimethyl-, 5,5'-dimethyl- and 4,4'-di-tert-butyl-dialkyl derivatives have been found to change colour from white or off-white to yellow in the presence of dimethylcadmium at concentrations as low as 13 ppm. The red form of mercury(II) iodide has been tested in both hydrogen and helium gas streams and found to change colour to yellow or white in the presence of gaseous di-iso-propyltelluride at concentrations as low as 1.5 ppm. This form of mercury(II) iodide also reacts photochemically with Me2Hg in a helium or hydrogen gas stream down to a concentration of 37 ppm. (C) 2004 Elsevier B.V. All rights reserved.