Calix[4]arenes bearing photoactive α-ketophosphonic acid groups at the upper rim of the macrocycle were synthesized and evaluated as inhibitors of glutathioneS-transferases. Irradiation at 365 nm increased the inhibition effects of some macrocyclic compounds on GSTP1-1 by more than two orders of magnitude. Calix[4]arene bis-α-ketophosphonic acids substituted at the lower rim by n-propyl or n-butyl