Three new thio­semi­car­ba­zide derivatives are described in terms of synthesis, structure and biological activity. N′-(Morpholine-4-carbono­thio­yl)-4-(4-phenyl­piperazin-1-yl)picolinohydrazonamide 2-methyl­tetra­hydro­furan hemisolvate, 2C21H27N7OS·C5H10O, 1, determined at 100 K, has ortho­rhom­bic (Pca21) symmetry and exhibits disorder. 4-(4-Phenyl­piperazin-1-yl)-N′-(piperidine-1-car­bono­thio­yl)picolinohydrazonamide–di­methyl­formamide–water (1/1/0.285), C22H29N7S·C3H7NO·0.285H2O, 2, determined at 100 K, has monoclinic (P21/c) symmetry. 4-(4-Phenyl­piperazin-1-yl)-N′-(pyrrolidine-1-carbono­thio­yl)pico­lino­hydrazonamide, C21H27N7S, 3, determined at 100 K, has triclinic (P1) symmetry and exhibits disorder. Compounds 1 and 2 contain solvent mol­ecules in their structure. All three studied com­pounds adopt the zwitterionic form and were tested for their microbiological activity on a model panel of Gram-positive and Gram-negative bacteria, as well as selected yeasts. Keywords: anti­bacterial activity; picolinohydrazonamide; crystal structure; thiosemicarbazide; biological activity.