Phthalazine diones that function as intracellular redox modulators and buffers are used to treat stressed cells in various disease states in which the intracellular redox status is impaired. By optimal buffering of aberrant redox states, phthalazine diones enhance the cellular processes essential for survival and augment the conventional or other external therapies necessary for treatment. The phthalazine diones of the invention thus regulate cell growth, differentiation, or death to serve as essential adjunctive therapy for the stressed host in various disease states.