Synthesis of various substituted 5-thio-2-pyridinecarboxylic acids and their derivatives is described by three methods, i.e., displacement of nitrite from methyl 5-nitro-2-pyridinecarboxylate (10) by a thiol anion, alkylation of methyl 5-thio-2-pyridinecarboxylate derived from reaction of the diazotized methyl-5-amino-2-pyridinecarboxylate (5) with thiocyanate followed by borohydride reduction of the product, and alkylation of 5-thio-2-pyridinecarbonitrile followed by hydrolysis. 5-Thio-2-pyridinecarbonitrile was obtained from butyl 6-methyl-3-pyridyl sulfoxide (2) by nitrosation and dehydration of the oxime. Many of these 5-thio-2-pyridinecarboxylic acid derivatives were orally active antihypertensive agents in the spontaneously hypertensive rat. Optimization of the structural parameters for this activity yiedled 5-[m-trifluorobenzyl) thio]-2-pyridinecarboxylic acid (41) and its sulfoxide, 42. Further biological studies with these compounds are described.