Abstract: Hypoxia selective cytotoxins having the structural formula ##STR1## wherein D, E, F and G, independently, are carbon or nitrogen, with the proviso that three or more of D, E, F and G are carbon; R.sub.1 and R.sub.2, independently, are selected from the group consisting of methyl, halo, hydro, trifluoromethyl, methoxy, cyano, and methylsulfo; R.sub.3 and R.sub.4, independently, are selected from the group consisting of methyl, ethyl, phenyl, naphthyl, tertiary butyl, halo, halomethylene, hydro, trifluoromethyl, cyano and methylsulfo; n is an integer 1 through 5; X is carbon or nitrogen; and Z is a physiologically acceptable anion, are disclosed. The compounds are useful as radiosensitizers or chemosensitizers, especially in the treatment of cancer patients.