2,4-Pyridinedicarbohydrazide 3 was used in synthesizing several new heterocyclic compounds with expected potential biological activity, via its reaction with various chemical reagents. A series of bis-(arylmethylidene)pyridine-2,4-dicarbohydrazides 4a-e were synthesized by condensation of 3 with various aldehydes. Further, replacement of the dicarbxylic acid functionality of 1 with five membered heterocycles, in the hope of obtaining additional pharmacological activity, encouraged us to synthesize some 2,4-bis-{pyrazolyl 5; pyrazolonyl 6; 1,3,4-oxadiazolyl 7, 9, 11, 14; 1,2,4-triazolyl 15 and triazolo[3,4-b][1,3,4]thiadiazinyl 17}pyridines.The structures of the synthesized products were identified by elemental analysis, MS, IR and ¹H NMR spectroscopy. The synthesized compounds were screened for their in vitro growth inhibiting activity against different strains of bacteria and compared with the standard antibiotic (Chloramphenicol) at triplicate concentration (5, 2.5,1 μg/ml). Also, they were screend for their in vivo anti-inflammatory activity [% Inhibition of oedema and % inhibition of plasma prostaglandin (PGE₂)] and anti-allergic activity (anti-histamine). Their toxicity (ALD₅₀ mg kg⁻¹ p.o.) and ulcerogenic (UD₅₀ mg kg⁻¹ i.p.) activities were measured and promising results were obtained.