(1R,2S,3R)-2-Acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)imidazole (THI) 1, a constituent of Caramel Colour III, has been found to depress blood lymphocyte counts in both mice and rats.[1]THI produces lymphopenia, apparently without toxic effects, in rats and mice and is able to affect the immune