Reversed-phase HPLC conditions for the separation of 4-(2-pyridyl)-1-piperazinethiocarboxylic acid 2-[1-(pyridyl)-ethylidene]hydrazide dihydrochloride (NSC 348977, I), a synthetic thiosemicarbazone with antitumor activity, from mouse plasma have been investigated. Following denaturization and precipitation of the spiked plasma with acetonitrile, an aliquot of the supernatant was diluted with aqueous buffer and subjected to analysis on a Nova-Pak C18 column (150 x 3.9 mm I.D.) by isocratic elution with 50 mM aqueous potassium phosphate buffer (pH 6.8, containing 1 mM EDTA)-acetonitrile (60:40, v/v). The column effluent was monitored for UV absorption at 310 nm. Problems identified in the sample preparation and separation of I include sensitivity to oxygen, light, non-neutral pH and the presence of metal ions. These factors were seen to adversely influence sample recovery, and attempts were made to find conditions which minimize their effects.