The document reports on the electron spin resonance (ESR) spectra of the 1,8-dihydroxy-9-anthron-10-yl radical and its deuterated isotopomers. This radical is believed to be involved in the mechanism of action of dithranol (anthralin), a drug used to treat psoriasis. ESR spectra were obtained by photolysis or thermal decomposition of dithranol or its dehydrodimer. The spectra matched what was expected for the authentic 1,8-dihydroxy-9-anthron-10-yl radical based on its hyperfine coupling constants. Spin adducts were also observed when the reactions were performed in the presence of a spin