Methods of employing bis(thio-hydrazide amides) to increase NK cell activity in a subject in need thereof, e.g., a subject with an infection or an immunodeficiency, are provided such that the disorder is not cancer, a proliferative cell disorder, a non-infective heat shock protein 70 (Hsp70) responsive disorder, or a proteasome-inhibitor responsive disorder. Typically, a subject, e.g., a human, can be in need of increased NK cell activity has an immunodeficiency or is treated for an infection (e.g., a bacterial, viral, fungal, or parasite infection, or a combination thereof). The method includes administering to the subject an effective amount of a compound represented by Structural Formula I: Y is a covalent bond or an optionally substituted straight chained hydrocarbyl group, or, Y, taken together with both >C=Z groups to which it is bonded, is an optionally substituted aromatic group. R.sub.1-R.sub.4 are independently --H, an optionally substituted aliphatic group, an optionally substituted aryl group, or R.sub.1 and R.sub.3 taken together with the carbon and nitrogen atoms to which they are bonded, and/or R.sub.2 and R.sub.4 taken together with the carbon and nitrogen atoms to which they are bonded, form a non-aromatic heterocyclic ring optionally fused to an aromatic ring. R.sub.7-R.sub.8 are independently --H, an optionally substituted aliphatic group, or an optionally substituted aryl group. Z is O or S. ##STR00001##