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Various substituted pyridine-2-carboxaldehyde thiosemicarbazones (12 compounds) have been synthesized and evaluated for antineoplastic activity in mice bearing the L1210 leukemia. Oxidation of 3-nitro-2-picoline,5-nitro-2-picoline,3-nitro-2,4-lutidine, and 5-nitro-2,4-lutidine with selenium dioxide was employed to generate the corresponding pyridine-2-carboxaldehydes, which were then converted to cyclic ethylene acetals and subsequently reduced to amino and hydroxyamino derivatives by catalytic hydrogenation. Condensation of nitro aldehydes and acetals with thiosemicarbazide afforded the respective thiosemicarbazones. Acetylation of the amino acetals and alkylsulfonation of the 5-amino acetal, followed by condensation with thiosemicarbazide was employed to yield amide thiosemicarbazones. The most active compounds synthesized were 3-aminopyridine-2-carboxaldehyde thiosemicarbazone and 3-amino-4-methylpyridine-2-carboxaldehyde thiosemicarbazone which produced against the L1210 leukemia, % T/C values of 246 and 255, and 40% 60-day long-term survivors at two daily doses of 40 mg/kg and 10 mg/kg, respectively, for six consecutive days.